Bug 1880679 [wpt PR 44632] - Adjust getHTML behavior to match recent consensus, a...

Bug 1880679 [wpt PR 44632] - Adjust getHTML behavior to match recent consensus, a=testonly

Automatic update from web-platform-tests
Adjust getHTML behavior to match recent consensus

This includes two changes:

1. Rename includeShadowRoots to serializableShadowRoots
2. Do not throw an exception if serializableShadowRoots is false
   but shadowRoots is non-empty.

I also added IDL defaults for both parameters to clean up the C++.
I also added a test of the use counter for getHTML().

Bug: 41490936
Change-Id: Ieedd81b5165d9652c3a7b68dea4a4fa5fb088560
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5304121
Auto-Submit: Mason Freed <masonf@chromium.org>
Commit-Queue: Mason Freed <masonf@chromium.org>
Reviewed-by: Di Zhang <dizhangg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1262930}

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wpt-commits: 503ce0a4b4f45201adb94c537345ee2d20661290
wpt-pr: 44632