[Partitioned Popins] Implement popinContextTypesSupported() JS API
This CL implements window.popinContextTypesSupported() that returns
the supported popin context types.
Explainer: https://explainers-by-googlers.github.io/partitioned-popins/
I2P: https://groups.google.com/a/chromium.org/g/blink-dev/c/ApU_zUmpQ2g/
Low-Coverage-Reason: COVERAGE_UNDERREPORTED Tested through WPTs.
Bug: 340606651
Bug: b/362973176
Change-Id: I02b2a75778610a5d23ca929b328fbcdd21fa9403
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5822620
Reviewed-by: Ari Chivukula arichiv@chromium.org
Reviewed-by: Daniel Cheng dcheng@chromium.org
Commit-Queue: Sandor «Alex» Major sandormajor@google.com
Reviewed-by: Robert Kaplow rkaplow@chromium.org
Cr-Commit-Position: refs/heads/main@{#1350876}