quic/stream: create gen. getWriter for stream/iter - #66513

Review requested:

• @nodejs/quic

@jasnell @pimterry
That is a first idea of how to move get writer out of QuicStream .
After the interface is discussed and agreed upon, I would then, in another commit, move the code for this part to a place related to stream/iter (where?).
We also need to discuss whether this should remain an internal method or part of the public api.
(In this case, additional checks are necessary)

P.S.: There seem to be some bugs remaining. (I thought I had run all tests, but it seems that I only ran lint and not a full build.) But discussing the structure should work anyway.

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.46%. Comparing base (8c1a7d3) to head (5393b34).
⚠️ Report is 23 commits behind head on main.

@@            Coverage Diff             @@
##             main   #66513      +/-   ##
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+ Coverage   90.45%   90.46%   +0.01%     
==========================================
  Files         791      792       +1     
  Lines      276806   276915     +109     
  Branches    53190    53199       +9     
==========================================
+ Hits       250373   250503     +130     
+ Misses      16842    16826      -16     
+ Partials     9591     9586       -5     

Ok, now, everything works according to the local tests.

I do not understand the build failures. It complains about an unknown compiler option? Do I need to rebase?

Looks like yes - it's complaining about --allow-overwriting-for-next-flag which I can see has since been dropped: #66524. Looks like this all relates to a recent V8 update.

That said, you'll then run into a separate issue, because that same V8 update has also independently broken the QUIC build 😆. Fix for that landing shortly, it's here: #66603

I have moved getWriter a separate file. It is not in the right place; I think it should go somewhere in the stream/iter dirs.

(I have not rebased, as the fixes for building quic are not on main yet).