Address remaining cases of unsafe buffers in ozone/wayland

This CL continues the effort to address the security team's initiative
to eliminate out-of-bounds errors in Chromium and enable the
`-Wunsafe-buffer-usage` compiler warning in ozone/wayland. The previous
CL (5717935) addressed some of the changes, but left some files excluded.

This CL aims to address the remaining cases that can be fixed and
document the ones that can't.

Bug: 353039516
Change-Id: If3f9b51545e351e27865c4d39b72dc2a452501a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5766157
Reviewed-by: David Benjamin <davidben@chromium.org>
Commit-Queue: Nick Yamane <nickdiego@igalia.com>
Reviewed-by: Nick Yamane <nickdiego@igalia.com>
Cr-Commit-Position: refs/heads/main@{#1343879}