Auto merge of #14211 - asajeffrey:constellation-share-more-script-threads, r=jdm

Share script threads by tab and by eTLD+1

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This PR shares script threads among all similar-origin documents in the same tab. This allows DOM object to be shared among same-origin same-tab documents.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #633.
- [X] These changes do not require tests because refactoring.

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tests/wpt/metadata/html/semantics/embedded-content/the-iframe-element/cross_origin_parentage.html.ini

@@ -1,8 +0,0 @@
-[cross_origin_parentage.html]
-  type: testharness
-  [Check the frame heriarchy 1]
-    expected: FAIL
-
-  [Check the frame heriarchy 2]
-    expected: FAIL
-