FileSystemAccess: Rename FileSystemAccessCapacityAllocationHost

This change renames FileSystemAccessCapacityAllocationHost to
FileSystemAccessFileModificationHost.

As part of this, all variables and filenames containing references to
*capacity_allocation* have been updated to *file_modification*.

Bug: 40284828
Change-Id: Ifdf4327adddaa02e0fb6c0398474d87f850e5fe1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5322681


Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Christine Hollingsworth <christinesm@chromium.org>
Reviewed-by: Austin Sullivan <asully@chromium.org>
Auto-Submit: Rahul Singh <rahsin@microsoft.com>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1266851}