Revert "WebUI: Remove unnecessary dependencies on js_library mojo targets"

This reverts commit 4fd20fd1e317915bea329ed2c48524b1e94fea15.

Reason for revert: https://ci.chromium.org/ui/p/chromium/builders/ci/Linux%20Chromium%20OS%20ASan%20LSan%20Builder/65254/overview

Original change's description:
> WebUI: Remove unnecessary dependencies on js_library mojo targets
>
> <target_name>_webui_js is actually a js_library() target, and is not
> responsible for generating any JS files (including .mojom-webui.js
> files). However, it is used as a proxy for the target generating such
> files in a lot of places.
>
> Things like copy() or grit() that are directly handling the generated
> mojo files should instead be relying on mojo targets that are
> responsible for generating those files, which have the form
> <mojo_target_name>_js__generator.
>
> This is in preparation for removing generation of such targets on
> non-ChromeOS platforms.
>
> Bug: 1316438
> Change-Id: Ia902fc5f888bf11b3f3d84406034e15dc151d972
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4029046
> Reviewed-by: Connie Wan <connily@chromium.org>
> Reviewed-by: Florin Malita <fmalita@chromium.org>
> Reviewed-by: Sophie Chang <sophiechang@chromium.org>
> Auto-Submit: Rebekah Potter <rbpotter@chromium.org>
> Commit-Queue: Connie Wan <connily@chromium.org>
> Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
> Reviewed-by: Peter Beverloo <peter@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1073047}

Bug: 1316438
Change-Id: I8effdc504db732098e14c37574b2b6e1d0248b5e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4035055
Quick-Run: Mike Wasserman <msw@chromium.org>
Auto-Submit: Mike Wasserman <msw@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Mike Wasserman <msw@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1073070}