webidl: fix existing and add missing buffer source converters

[Renegade334]

This relates to...

Aims to provide support for a resolution for #4495.

Rationale

Factors contributing to the specification divergence for fetch/websockets as detailed in the linked issue are:

• the required buffer source converters are missing;
• the existing buffer source converters are not used within the codebase;
• those that do exist are out-of-date with the IDL standard.

Changes

Changes to existing converters:

• ArrayBuffer used to convert to either ArrayBuffer or ArrayBuffer | SharedArrayBuffer, depending on the presence or absence of the [AllowShared] attribute. Subsequent changes to the standard have separated these out into separate IDL types, and so this converter has been split into two.
• The ArrayBuffer and SharedArrayBuffer converters correctly handle the presence or absence of the [AllowResizable] attribute.
• The remaining buffer source converters correctly handle the presence or absence of the [AllowShared] and [AllowResizable] attributes.

New converters:

• ArrayBufferView
• BufferSource
• AllowSharedBufferSource

Breaking Changes and Deprecations

As mentioned, this does not affect the current behaviour of undici web APIs, as they do not use these converters at present.

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

[KhafraDev]

This won't fix the issue, but as you mentioned, provides a resolution to fixing it. Thanks!