Handles are notorious for preventing compiler optimizations. We should
avoid them for simple const functions.

- Mark more API functions const
- Mark more String functions const

Bug: v8:11195, chromium:808503, v8:11263
Change-Id: I9940e85600bc7d19027039d807b3313e2dcccdc7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2575065Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73159}