spanify: Renewed arrayification (X/43)

This CL is part of the wider spanification / arrayification effort [1]
and does not (intentionally) introduce behavioral change. It applies the
`std::array` rewrite to

ui/events

as close as possible to the output directly written by `spanify`, with
no hand-rolled fixes (except where rebasing would require).

This change (and its siblings taken together) is thought not to cause
any measurable perf regressions [2].

[1] https://issues.chromium.org/356643982
[2] https://docs.google.com/document/d/1jughaR6JKn7T-dDjMou10awyNkhE5T-vLY_K2YMqHE4/edit?tab=t.0#heading=h.r2eguxl5lhu7

This CL was uploaded by git cl split.

Bug: 406029216
Change-Id: If4d5506215bf72fe2ec792fa4cbad3ede23bbbf1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6477685
Commit-Queue: Alex Gough <ajgo@chromium.org>
Reviewed-by: Alex Gough <ajgo@chromium.org>
Reviewed-by: Stephen Nusko <nuskos@chromium.org>
Auto-Submit: Kalvin Lee <kdlee@chromium.org>
Owners-Override: Alex Gough <ajgo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1450833}