WebUI: Infer chrome://resources/ path_mappings from deps in ts_library.

This will help eliminate missing dependencies, which often have been the
source of transient/flaky build errors.

Previously missing dependencies would go uncaught and opened the door
for flaky build errors on bots, when the order of ts_library() target
execution happened differently.

After this CL, any missing dependencies to ts_library() targets under
ui/webui/resources/ will result in a consistent build time error.

Bug: 1402829
Change-Id: I27b7859b07f2b4061d949370a6287a637aa224d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4194970
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1099586}