Partition Blob URL revocation by Storage Key

[recvfrom]

Part of the changes discussed in #153 (comment)

This updates URL.revokeObjectURL to not allow revoking a Blob URL except from contexts with the same Storage Key as the one in which the Blob URL was created. A corresponding PR will update the Fetch spec to incorporate similar Storage Key checks into Blob URL fetches.

I considered incorporating the Storage Key checks into the "resolve a blob URL" algorithm instead, but it seemed that this would require an environment settings object to be available as part of https://url.spec.whatwg.org/#url-parsing, and I'm not sure whether that is the case / a change we want.

For normative changes, the following tasks have been completed:

• Modified Web platform tests (link to pull request)

• https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/web_tests/external/wpt/FileAPI/BlobURL/cross-partition.tentative.https.html

Implementation commitment:

• WebKit - Already implemented partitioning by top-level origin, considering partitioning by top-level site - Blob URL store partitioning #153 (comment)
• Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=40057646)
• Gecko - Already implemented - Blob URL store partitioning #153 (comment)

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[miketaylr]

Mind taking a look @mkruisselbrink?