extensions: Add inputs for grit actions

Goal of this CL is to make the grit action runs on remote worker so that
we can reduce local resource usage and share build cache between
bots/developers. But we need to tell which files are read by grit
actions to siso from build system layer.

Although we need to specify inputs both in grit and BUILD.gn, I'll add a
check to detect which files are missed or overspecified in grit.py and
we can now rely on AI agent to fix them easily.

Extracted from https://crrev.com/c/8085243.

Bug: 535044365
Change-Id: Iae4b703bfbab416b6a881f2347aaf80bdcfc2732
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/8181089
Reviewed-by: Andrea Orru <andreaorru@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Devlin Cronin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1673832}