components/crx_file: fix unsafe buffers

This change removes unsafe buffer warnings in components/crx_file,
except for those in crx_build_action_main.cc. To do that, this change:

* Replaces most uses of plain arrays with std::array
* Replaces uses of file and other APIs that accept (pointer, length)
  pairs with variants that accept spans
* Simplifies a bit of related code using newer APIs (especially
  base::File::*AndCheck and std::ranges::search)

This is a preparatory refactor for migrating components/crx_file to new
crypto APIs.

Change-Id: I81773202a5aaa00933fb0db6d181d28f7cc215dc
Bug: 372283556
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6441646
Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Commit-Queue: Elly FJ <ellyjones@chromium.org>
Reviewed-by: Devlin Cronin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1446861}