arrayify: Prefer `constexpr`

This CL is intended to be trivial. It marks the return from `std::to_array` as
`constexpr`. This CL is a split of a naive textual search-and-replace under:

components/browsing_topics

This CL was uploaded by git cl split.

Change-Id: Iee5202bcdb36cd0fe0a0a757898b2c92c4764b26
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6301470
Auto-Submit: Kalvin Lee <kdlee@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1424364}