[PDF Ink Signatures] Add brush color strings, labels, and titles

Add new PDF strings for brush colors without existing strings. Use the
existing strings and these new strings to add aria labels and titles to
the brush color buttons.

NO_IFTTT=Only the labels were changed, not the actual brush color
values.

Bug: 358407363
Change-Id: I376092ddc3cbd32b38ad4019e6e04cd304f8a1d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6055185
Reviewed-by: Lei Zhang <thestig@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Andy Phan <andyphan@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1392528}