Bug 1915764 [wpt PR 47881] - DOM: Fix Observable#from() [Symbol.ite…

…rator] semantics (1/2), a=testonly

Automatic update from web-platform-tests
DOM: Fix `Observable#from()` [Symbol.iterator] semantics (1/2)

See WICG/observable#160, which specs the
`Observable#from()` semantics, matching these tests. See also
https://crbug.com/363015168 which describes the ways in which our
current implementation of `Observable#from()`'s detection semantics
are overbroad.

This CL makes the implementation of the "detection semantics" match the
desired behavior outlined in that issue, and adds a bunch of tests.

R=masonfchromium.org

Bug: 363015168, 40282760
Change-Id: Id6cfdd45c44286b298e107635e4283b018f50aaf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5824955
Commit-Queue: Dominic Farolino <domchromium.org>
Reviewed-by: Mason Freed <masonfchromium.org>
Cr-Commit-Position: refs/heads/main{#1349019}

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wpt-commits: e74098ed10aa0a4fc6ad6b8d6e354895addd00d1
wpt-pr: 47881

UltraBlame original commit: ef2aac8ce3d8e023f93a55c7593551be16b64d72