stream: fix Writable.toWeb() desiredSize for non-object-mode

[mcollina]

Writable.toWeb() used a plain { highWaterMark } as the queuing strategy for non-object-mode streams, which meant no size function was provided. The WritableStream defaulted to counting each chunk as size 1, so desiredSize was incorrect (e.g. a 3-byte Uint8Array was counted as size 1 instead of 3).

Add a size() function to the strategy that mirrors how the Node.js stream computes chunk length: byteLength for typed arrays, length for strings/buffers, falling back to 1.

Fixes: #56269

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.32%. Comparing base (74ccf38) to head (088b5e2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #62986      +/-   ##
==========================================
- Coverage   90.32%   90.32%   -0.01%     
==========================================
  Files         730      730              
  Lines      234209   234157      -52     
  Branches    43934    43906      -28     
==========================================
- Hits       211558   211508      -50     
- Misses      14372    14378       +6     
+ Partials     8279     8271       -8     

Files with missing lines	Coverage Δ
lib/internal/webstreams/adapters.js	86.62% <100.00%> (+0.06%)	⬆️

... and 35 files with indirect coverage changes

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[Renegade334]

Add a size() function to the strategy that mirrors how the Node.js stream computes chunk length: byteLength for typed arrays, length for strings/buffers, falling back to 1.

Technically, I think the Node.js side deals exclusively in .length, not that it should make a difference to the outcome.