[Spec] Allow setting automatic beacon data from cross-origin subframes.

[blu25]

This PR modifies the automatic beacon algorithms to support data being set from frames that are cross-origin to the fenced frame config's mapped URL. More specifically, this makes the following modifications:

• setReportEventDataForAutomaticBeacons() is modified to allow data to be set from cross-origin subframes, but only if the data's crossOriginExposed parameter is set to true.
• A new snapshot automatic beacon mapping type is introduced that contains 2 mappings. The first mapping is the same as the existing automatic beacon data map. The second mapping only contains automatic beacon data whose crossOriginExposed parameter is set to true. This is needed since, as part of this change, cross-origin subframes that trigger automatic beacons will now use the first cross-origin exposed data it finds up the frame tree, versus the first data it finds regardless of whether it is cross-origin exposed or not (which it wouldn't be able to use).
• The attempt to send an automatic beacon algorithm now checks either the "all data mapping" or the "cross-origin only mapping" based on whether the automatic beacon initiator is cross-origin to the fenced frame config's mapped URL. This will ensure that if an ancestor has usable data, it won't accidentally grab data from a closer ancestor that can't be used. This also has a side effect of letting us remove the |should send beacon with data| variable, as the same behavior is now obtained by simply checking the cross-origin only data mapping.
• The get the automatic beacon data mapping to use is renamed and modified to read data into both the regular mapping and the cross-origin only mapping.

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Preview | Diff

[domfarolino]

This is blocking merge right?

[blu25]

Yeah. This isn't ready for review yet. I just uploaded this so I could see a visual diff.

I'm also running into issues with the tests not being found. I tried running bikeshed update --skip-manifest and got this error:

FATAL ERROR: Bikeshed currently only knows how to handle WPT v8 manifest data, but got v9. Please report this to the maintainer!

I think I have the latest release installed (4.2.8) so adding any new WPTs to the spec might be blocked until that gets patched.

[VergeA]

Looks good now, thanks! Assuming it compiles after the Bikeshed fix you're waiting on goes in.

[domfarolino]

I'm happy to defer to @VergeA's review here since the annals of the cross-origin automatic beacon work is slightly beyond me at this point, but from looking at the PR nothing major sticks out.