Adds const modifiers to several methods and their parameters in
AllocationStats, BasicMemoryChunk and ReadOnlySpace.

Also moves BasicMemoryChunk::OffsetToAddress to ReadOnlyPage.

Bug: v8:10454
Change-Id: Ibda8f9212d95dff71ed1d8f1f985eb1c7e6087aa
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2284986
Commit-Queue: Dan Elphick <delphick@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Auto-Submit: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68721}

This moves several fields that will be needed by ReadOnlySpace pages
when it stops using MemoryChunk into BasicMemoryChunk.

Additionally AllocationStats is moved from spaces.h into
allocation-stats.h.

Bug: v8:10473, v8:10454
Change-Id: I76a66565a260126e629bd7588a5418267dfa8423
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2228722Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68134}