[Desktop Android CRX] Enable more tests in ExtensionWebRequestApiTest.

This cl includes the following changes:

1. Add embedded_test_server() support in ExtensionPlatformApiTest.

2. Port ExtensionWebRequestApiTest.ListenersInMultipleContexts
on desktop android platform. More tests will be ported in the
follow up cls.

This CL affects only tests, should have no behavior change.

Bug: 371324825
Change-Id: I30ba2ff99113b7d7b42d3f9b3e7ba8c9a26ca580
Cq-Include-Trybots: luci.chromium.try:android-desktop-arm64-compile-rel,android-desktop-x64-compile-rel,android-desktop-14-x64-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6007302
Commit-Queue: Jenny Zhang <jennyz@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1382060}