Bug 1877566 [wpt PR 44300] - DOM: Implement the forEach() Observabl…

…e operator, a=testonly

Automatic update from web-platform-tests
DOM: Implement the `forEach()` Observable operator

This CL implements the semantics specified in
https://wicg.github.io/observable/#dom-observable-foreach.

See WICG/observable#105.

For WPTs:
Co-authored-by: benbenlesh.com

R=masonfchromium.org

Bug: 1485981
Change-Id: I61344bad7fa4bac65146e1305a376fc1f5e55dc3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5249869
Reviewed-by: Mason Freed <masonfchromium.org>
Commit-Queue: Dominic Farolino <domchromium.org>
Cr-Commit-Position: refs/heads/main{#1257328}

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wpt-commits: 910e4c850e0e43a1832f943e2782ffa8f06b3eb9
wpt-pr: 44300

UltraBlame original commit: b7468884afeb181ab7f2ec3224e73d56c0091360