[Partitioned Popins] Simplify RSA tests
These are getting out of hand, let's consolidate the read paths in
JavaScript at least.
Explainer: https://explainers-by-googlers.github.io/partitioned-popins/
I2P: https://groups.google.com/a/chromium.org/g/blink-dev/c/ApU_zUmpQ2g/
Bug: 340606651
Change-Id: I43ae4fcd338611c4d0cd918b3fdad6b59098fd22
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5962496
Reviewed-by: Sandor «Alex» Major sandormajor@google.com
Commit-Queue: Sandor «Alex» Major sandormajor@google.com
Auto-Submit: Ari Chivukula arichiv@chromium.org
Cr-Commit-Position: refs/heads/main@{#1373485}