WebUI: Rename build_webui() non_web_component_files to ts_files, part1.

'non_web_component_files' is no longer an accurate name and a bit
confusing, since this list often holds web component files that have
their .html.ts template file checked-in as opposed to auto-generated,
which is the recommended approach for Lit-based elements.

In this part:
 - Updating build_webui() to support both old and new names.
 - Updating documentation to only document the new name.
 - Updating //ui/webui/resources/cr_components/BUILD.gn to use the new
   name.

Other client code will be updated in follow-up CLs.

Bug: 409590662
Change-Id: I5d75c9a78952ffa6a30c84bb5f0b90f2de10292c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6444534
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Auto-Submit: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1445422}