fix(textbox): Fix IME and touch editing on Android browsers (backport #25804) - #25984

Takes Uno's servicing/6.8 from 6951c2c up to 5254ace (42 pull
requests). Conflicts, by area:

IME and TextBox (unoplatform#25984, backport of unoplatform#25804; unoplatform#25952, backport of unoplatform#25619;
unoplatform#25976, backport of unoplatform#25818)
- Takes upstream's composition design (unoplatform#25804): the browser's input is
  the source of truth for the text, compositions included. This drops
  the composition parts of the unoplatform#24502 port (90746b8): its
  TypeScript composition handling, the StartIndex/TextChangePending
  event arguments, the IsReadOnly forwarding to the hidden input, and
  its Given_TextBox.BrowserSoftKeyboard tests.
- Keeps the non-IME browser fixes on top of it, in the form their
  master pull requests have on unoplatform#25804: Enter raised once per press and
  tracked by key code (unoplatform#25174, with Given_TextBox.BrowserEnterKey from
  master in place of the Enter tests that lived in the dropped file),
  the iOS refocus on tap (unoplatform#25185), pastes without text and isIOS from
  BrowserInputHelper.
- Moves the unoplatform#26005 MaxLength fixes onto unoplatform#25804's native input path, as
  master has them: a refused browser edit keeps the TextBox's selection,
  TextBoxView.UpdateTextFromNative reports whether the edit went in, and
  the IME keeps its range on the applied text (master be85699, which
  d226897 had ported onto the unoplatform#24502 IME). Adds that commit's browser
  and platform-applied IME tests.
- TextBox.pointers.skia.cs: upstream's file (unoplatform#25619 iOS touch editing,
  unoplatform#25818, unoplatform#25804), with the unoplatform#25126 port (the hold acts when it starts,
  a touch right-tap keeps the caret) in the form master's unoplatform#25126 branch
  has it on unoplatform#25619, including focusing before the iOS hold timer acts
  and its iOS not-focusable test.

Pointers (unoplatform#25976, backport of unoplatform#25818)
- Tapped and RightTapped are raised once the PointerReleased bubbled
  (unoplatform#25818), with the unoplatform#25732 port's window coordinates (2-argument
  routed event args, RawPosition for ContextRequested), as master's
  unoplatform#25732 branch has them.
- The release wrapper of unoplatform#25818 keeps the unoplatform#25126 port's
  StopContextMenuTimer at the start of the release.

DependencyObject (unoplatform#26142, backport of unoplatform#26123)
- Takes upstream, then the code of unoplatform#25839 (97a2f17), which replaces
  this branch's unoplatform#25102 ports (800247f, be41da6, fd40bf9,
  7546379). DependencyObjectStore.Binder.cs, .alc.cs,
  Application.Alc.cs, ResourceDictionary.alc.cs and their tests now
  match unoplatform#25839; this drops 800247f's own
  SingleParentNonFE_Parent_Removes_Value_Then_Next_Parent_Starts_Clean
  test, which unoplatform#25839 doesn't have.

Imaging (unoplatform#25597, unoplatform#25915, unoplatform#25911, unoplatform#25897)
- Keeps this branch's side: it has the later forms of these fixes
  (unoplatform#25124, unoplatform#25559, unoplatform#25633 and unoplatform#26370 ports), where upstream has the
  6.8-only unoplatform#25597 design and earlier snapshots. Upstream's shared
  download, IgnoreImageCache and failed-load fixes are covered by
  SharedImageDecode. Adds upstream's When_Source_Outlives_Brushes test.

ToolTip (unoplatform#26098, backport of unoplatform#25137 and unoplatform#26096)
- Keeps this branch's unoplatform#25137 port and adds unoplatform#26096 in master's form: the
  service releases only a ToolTip it opened, and leaves one the app
  opened during the show delay to the app. Keeps both sides' tests.

Flyout (unoplatform#26062, backport of unoplatform#26060)
- This branch had the same commits already; keeps the "Keep
  non-resizable flyouts in window" port and its tests.

Also removes a helper pair in Given_AccessibleTextBox that both sides
added.

Port of unoplatform#26434 (for unoplatform#26432), commits
faba3ed, 096daef, 8e2644f, b8d2189, edce6fa and
6939ef4, onto the unoplatform#25804 IME design this branch takes
from servicing/6.8 (unoplatform#25984).

- TextCompositionChanged for text the platform applied (WebAssembly,
  Skia Android) waits for the platform's text sync, and isn't raised
  for an update the TextBox refused. The Changed and no-commit Ended
  ranges are clamped to the text. Skia Android reports where its
  composing region starts.
- A composition ends when the hidden input is replaced or detached.
- An edit a BeforeTextChanging handler or a read-only TextBox refuses
  is written back to the input at once, ending the composition.
  Unlike master, this branch does the same for an edit MaxLength
  refuses or a TextChanging handler changes (see below).
- The hidden input is read-only with the TextBox.
- The caret goes back at once after a refused edit.

6.8 differences:
- Master's TextBoxCore.IME.cs, .Input.cs and .cs changes go to
  TextBox.IME.skia.cs, TextBox.skia.cs and TextBox.cs; events are raised
  on the TextBox itself. There is no RichEditBox IME, partial commit or
  CompositionCanceled on 6.8, so those parts are left out.
- Skia Android syncs through a new TextBox.UpdateTextFromNative, the
  6.8 counterpart of master's IImeSessionHost.UpdateTextFromNative. It
  raises the held TextCompositionChanged, and compares the editable's
  \n line breaks as the TextBox's \r, as master's
  IsNativeEchoOfCurrentText does.
- The read-only input follows TextBox.IsReadOnly through
  OnIsReadonlyChangedPartial; UpdateProperties, which only sets the
  enter key hint on 6.8, now also sets readOnly or re-enters the input.

With this branch's port of unoplatform#26005 (be85699):
- A refused platform sync puts the composition range back on the text
  that is there (unoplatform#26005), and raises TextCompositionChanged
  for that range only when it isn't the last range raised. The refused
  update's own range is never raised (unoplatform#26434).
- While a composition holds text the TextBox refused past MaxLength
  (reconciled when it ends), the hidden input's selectionchange isn't
  reported: its offsets are in that text, not in the TextBox's. Without
  this, the input's caret replaced the one edce6fa restores at once.
- ApplyNativeInput keeps unoplatform#26005's handling of a refused
  edit's pending selection.

Like Android's own LengthFilter (and this branch before the catch-up),
a composition edit the TextBox doesn't keep as the keyboard applied it
(MaxLength, a TextChanging filter, as well as BeforeTextChanging and
read-only) writes the TextBox's text back at once and ends the
composition, on WebAssembly and on Skia Android. Master keeps a
MaxLength or TextChanging refusal in the input until the composition
ends, so a CJK conversion can bring it back within the limit. Gboard
composes every Latin word, though, so the refused letters stayed in the
input for the whole word: its suggestions were built on them, and
Backspace deleted them before it reached the TextBox's text. A
conversion past the limit is lost here, as with Android's LengthFilter.
When_Browser_Ime_Composes_With_TextChanging_Filter (unoplatform#25804)
and the two conversion tests of unoplatform#26434 now expect that,
and When_Browser_Ime_Composes_Word_Past_MaxLength_Then_Input_Keeps_The_Limit
covers the Gboard case.

Adds tests for a refused Skia Android sync, \n line breaks in its sync,
and a refused composition followed by another before the dispatcher
runs.