Rename Time::kTimeTToMicrosecondsOffset to kMicrosecondsFromWindowsToUnixEpoch

Bug: 355423207
Change-Id: I5d9edbbc461d8c0ee9cb991e4239d9a1674e343f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/8040566
Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Owners-Override: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1657178}
NOKEYCHECK=True
GitOrigin-RevId: af8aa1ae8a505f9695c95153fb08b8058ca5f14d