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

net

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 an experimental version of git cl split
(https://crbug.com/389069356).

Bug: 406029216
Change-Id: I2c7d81dd3c3d712077fbc6ef13a787bae28bcea9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6436855
Owners-Override: Alex Gough <ajgo@chromium.org>
Reviewed-by: Alex Gough <ajgo@chromium.org>
Commit-Queue: Alex Gough <ajgo@chromium.org>
Auto-Submit: Kalvin Lee <kdlee@chromium.org>
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1449537}