http2: expose writable stream state on compat response

[cookesan]

Fixes: #63000

This adds the missing writableObjectMode and writableNeedDrain getters to Http2ServerResponse in the HTTP/2 compatibility layer. The getters mirror the underlying stream, matching the existing writable state properties.

The writable-properties test now covers both properties.

Tests:

• ./configure --ninja
• ninja -C out/Release node
• git diff --check
• ./out/Release/node --check lib/internal/http2/compat.js
• ./out/Release/node --check test/parallel/test-http2-res-writable-properties.js
• python3 tools/test.py --mode=release test/parallel/test-http2-res-writable-properties.js
• python3 tools/test.py --mode=release test/parallel/test-http2-res-writable-properties.js test/parallel/test-http2-compat-serverresponse.js test/parallel/test-http2-compat-serverresponse-finished.js test/parallel/test-http2-compat-serverresponse-drain.js
• make lint-js LINT_JS_TARGETS="lib/internal/http2/compat.js test/parallel/test-http2-res-writable-properties.js"

[nodejs-github-bot]

Review requested:

• @nodejs/http2
• @nodejs/net

[mcollina]

lgtm

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/72975/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.67%. Comparing base (4e3a873) to head (ab628ad).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63003      +/-   ##
==========================================
- Coverage   91.47%   89.67%   -1.81%     
==========================================
  Files         357      707     +350     
  Lines      150883   219517   +68634     
  Branches    23778    42089   +18311     
==========================================
+ Hits       138026   196842   +58816     
- Misses      12582    14579    +1997     
- Partials      275     8096    +7821     

Files with missing lines	Coverage Δ
lib/internal/http2/compat.js	96.96% <100.00%> (+0.02%)	⬆️

... and 471 files with indirect coverage changes

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