This CL adds a lint error for variables that are unnecessarily bound
with 'let' when they could be bound using 'const. This test is skipped
for struct types. For struct types, the "constness" also depends on
the struct methods called and whether these methods write to the struct
or not. This is not straight-forward to detect.

Drive-by: Fix all the newly introduced lint errors.

Bug: v8:7793
Change-Id: I0522ffcc4321350eef2e9573b8430bc78200ddce
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1645322
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62085}