FspCache: Evict file when GetMetadata and OpenFile observe new vTag

Also undo the changes added in CL:5556842 where the check for a new
version tag occurs in ReadBytes (from ReadFile) as this version tag
comes from the OpenFile result and the check now occurs as part of
OpenFile.

Test: unit_tests --gtest_filter=FileSystemProviderCloudFileSystemTest
Bug: b/339114823
Change-Id: Ie3f953bddebd1ebab5d6e2235c3abab4c32f5993
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5584556
Reviewed-by: Ben Reich <benreich@chromium.org>
Commit-Queue: Cassy Chun-Crogan <cassycc@google.com>
Cr-Commit-Position: refs/heads/main@{#1309134}