Switch trusted types sinks to use union type

[lukewarlow]

Switch Trusted Types sinks to use union IDL type

After recent discussions we've decided to change trusted types to use union IDL types across all sinks. This requires changes to the IDL and algorithms for the various sinks.

• [x] At least two implementers are interested (and none opposed):
  • Gecko https://github.com/mozilla/standards-positions/issues/20
  • Chromium
• [x] Tests are written and can be reviewed and commented upon at:
  • https://wpt.live/trusted-types
  • https://github.com/web-platform-tests/wpt/pull/46185/
• [x] Implementation bugs are filed:
  • Chromium: https://issues.chromium.org/issues/340822358
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=1508286 - meta bug
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=273412
• [ ] MDN issue is filed: …
• [x] The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

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/dom.html ( diff ) /dynamic-markup-insertion.html ( diff ) /iframe-embed-object.html ( diff ) /infrastructure.html ( diff ) /workers.html ( diff )

[lukewarlow]

Needs https://github.com/whatwg/html/pull/10282 and https://github.com/whatwg/html/pull/10283 merged first to avoid needing to do work on the DOMParsing spec as well.

[zcorpan]

The diff view shows document.write and writeln with HTMLString. I suppose this needs to be rebased so that #10199 is included, and update those to union type here.

[lukewarlow]

I've rebased atop the document.write PR and removed the strings from this PR

[lukewarlow]

@zcorpan @annevk is this ready to be merged now it's rebased?