Introduce grd file for metrics URLs

Currently, metrics (UMA) URLs are stored in a cc file. Depending on if
this is a Chrome-branded build, a src-internal version of the cc file
will be used instead.

Unfortunately, that set up is not LGPL compliant. Instead, they should
be moved to resources/grd files.

This CL is the first part. It introduces the resources files, and adds
them to the various build targets that will need it.

Additionally, native WebView unit tests (`android_webview_unittests`
build target) don't currently load any resources, like other test
suites (e.g. `components_unittests`). Since some native WebView unit
tests will need to access the URLs/resources in this CL, this CL also
adds a resource initialization step to this test suite. I copied the
set up of other test suites to do this, e.g.
https://source.chromium.org/chromium/chromium/src/+/main:components/test/components_test_suite.cc

Bug: 358224254
Change-Id: I44efd5a50e5ded05318e61de594f35550df4dfae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5953911
Reviewed-by: Richard (Torne) Coles <torne@chromium.org>
Owners-Override: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Luc Nguyen <lucnguyen@google.com>
Cr-Commit-Position: refs/heads/main@{#1374261}