stream: rename Duplex.toWeb() type option to readableType

[Renegade334]

The webstreams standard uses the name readableType for a source property which specifies the type of the readable component of a constructed readable-writable pair.¹ Although this is only future-proofed nomenclature at the moment, we should probably follow this convention here, for consistency and just in case we also need to support WritableStream types in the future.

This paradigm would also be consistent with Duplex.toWeb() taking readableStrategy and writableStrategy options in the future, if so desired.

Because Duplex.toWeb() is no longer marked as experimental, I believe that removing options.type entirely would need a full deprecation cycle, so I've just turned it into a silent alias for simplicity.

Refs: #58664

Footnotes

1. https://streams.spec.whatwg.org/#dictdef-transformer ↩

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.75%. Comparing base (6c44d31) to head (c4fdc85).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61632      +/-   ##
==========================================
+ Coverage   89.73%   89.75%   +0.01%     
==========================================
  Files         673      673              
  Lines      203948   203954       +6     
  Branches    39193    39194       +1     
==========================================
+ Hits       183022   183051      +29     
+ Misses      13240    13239       -1     
+ Partials     7686     7664      -22     

Files with missing lines	Coverage Δ
lib/internal/webstreams/adapters.js	85.66% <100.00%> (+0.08%)	⬆️

... and 32 files with indirect coverage changes

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