Bug 1876659 [wpt PR 44216] - Add support for the shadow root clonable…

… flag, a=testonly

Automatic update from web-platform-tests
Add support for the shadow root clonable flag

This landed in the these two spec PRs:

  whatwg/dom#892
  whatwg/dom#1237

and was discussed here:

  whatwg/dom#1137
  whatwg/dom#1236

This CL adds support for clonable, behind a new ShadowRootClonable
flag. There was already a very basic test, but I added a few
more cases.

This should be fairly web compatible, but there is a risk since with
this feature enabled, declarative shadow roots in the main document
(as opposed to in a <template> element) will now be cloned. I will
launch this feature carefully. Safari has already shipped, and Gecko
has implemented this and plans to ship soon.

Chromestatus:
https://chromestatus.com/feature/5161435196030976

I2P:
https://groups.google.com/a/chromium.org/g/blink-dev/c/nZhPt0ePCAA

Bug: 1510466
Change-Id: Ie25b72f369ca0542555f91010b0f22d295403728
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5239277
Auto-Submit: Mason Freed <masonfchromium.org>
Reviewed-by: David Baron <dbaronchromium.org>
Commit-Queue: David Baron <dbaronchromium.org>
Cr-Commit-Position: refs/heads/main{#1253059}

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wpt-commits: adc1ac02e6d8e080508325ab4525bab8d09177a6
wpt-pr: 44216

UltraBlame original commit: c628961696861f1ee92fe22401f9f939d8df6a8d