extensions: Port ExtensionUpdater to desktop Android

This class is a dependency of other classes we're actively trying to
port to Android. The vast majority of the code in this class works on
Android, so #ifdef out the two parts that don't:
* CorruptExtensionReinstaller - will be ported soon, once its last
  dependency (ExternalProviderManager) is ported (and that dependency
  depends on this class, hence this CL).
* ExtensionManagement - we've decided to defer

Bug: 404943906
Change-Id: I66d41c83167812359a37e8190472c4fc32d72f1a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6421507
Reviewed-by: David Bertoni <dbertoni@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1441343}