Avoid including base/files/file_util.h in some headers.

Rarely would anyone ever use base/files/file_util.h functions inside a
header. Most code authors meant to include base/files/file_path.h or
forward declare base::FilePath. Do that and then add missing file_util.h
includes to fix the build.

Bug: 242216
Change-Id: I6280125f310cff0db1109c401d84e01aba386376
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3518311


Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Owners-Override: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#983450}
NOKEYCHECK=True
GitOrigin-RevId: 527964a214baed4f325c0d7751bfc527ba10bf34