Viewpoint / BCFTopics: BCF clipping planes are dropped by create(data) and load(), and clip the wrong half when they are made #863

Describe the bug 📝

A BCF clipping plane never reaches the scene through Viewpoints.create(data) or BCFTopics.load, and when one is made through set(), the opposite half of the model is cut off.

A BCF 3.0 file with one clipping plane (IFC Z = 7.5 m, direction up: the part above is cut off), imported. Left: the building cut through its windows. Right: BCFTopics.load + go(), no clipping plane.

The same plane given to set() on a viewpoint that has a world. Left: the part above the plane is cut off. Right: the part below.

• Dropped: set() creates clipping planes only when the viewpoint has a world. Viewpoints.create(data) runs set() in the constructor and gives the world only after it, and BCFTopics.load creates its viewpoints with new Viewpoint(components, data) and never gives them a world, even when Viewpoints.world is set. (Viewpoint.go() does nothing, silently, when the viewpoint has no world #842 describes the missing world for go(); the error fix(viewpoints): throw a clear error when go() has no world #843 adds would then fire for every imported viewpoint.)
• Inverted: the Viewpoint docs say the direction "points in the invisible direction meaning the half-space that is clipped", as BCF does. set() passes it to Clipper.createFromNormalAndCoplanarPoint as the normal, and a Clipper plane keeps the half its normal points to (the Clipper's own create() negates the face normal for that). toJSON() writes the normal back as the direction, so a round trip inside That Open matches, but every plane exchanged with another BCF tool clips the opposite half.
• Unread: load reads Location.x / Direction.x, but BCF-XML has <Location><X>…, and BCFTopics.xmlParser keeps the tag names, so every coordinate is undefined.
• Title (same method): set(data) runs this.title = data.title, so a set() without a title clears it, although the docs say the properties not given remain unchanged.

Writing the planes to .bcfv on export is listed in #825.

Expected: create(data) and load give the viewpoint its world before set() (or set() makes the planes once a world is given); the plane's normal is the opposite of the BCF direction (and toJSON() writes the opposite of the normal); load reads Location.X / .Y / .Z and the same for Direction; set() keeps the title when data.title is undefined.

BUG imported viewpoint has a world: got false, expected true
BUG imported viewpoint's clipping planes: got 0, expected 1
BUG Location.x, what load() reads: got undefined, expected 6
BUG title after set() without a title: got null, expected "Level 2"

System:
    OS: Windows 11 10.0.26200
    CPU: (16) x64 Intel(R) Core(TM) i9-10885H CPU @ 2.40GHz
    Memory: 33.34 GB / 63.76 GB
  Binaries:
    Node: 22.22.1 - C:\nvm4w\nodejs\node.EXE
    npm: 11.12.0 - C:\nvm4w\nodejs\npm.CMD
  Browsers:
    Chrome: 156.0.8078.48
    Edge: Chromium (152.0.4191.53)
  npmPackages:
    @thatopen/components: 3.6.0 => 3.6.0
    @thatopen/components-front: 3.6.0 => 3.6.0
    @thatopen/fragments: 3.6.0 => 3.6.0
    @thatopen/ui: 3.4.17 => 3.4.17
    camera-controls: 3.1.2 => 3.1.2
    three: 0.184.0 => 0.184.0
    web-ifc: 0.0.77 => 0.0.77