[iwa] Make sure all install/update cases are handled correctly.

This CL tries to ensure The Table (aka The Matrix) from here:
http://goto.google.com/iwa-install-precedence
resembles the truth and nothing but the truth.

What this introduces mainly is:
- If policy wants to install an app and the app has been installed
  previously (unmanaged or dev bundle), first we remove the installed
  app completely.
- If unmanaged or dev ui wants to install an app and the app has been
  installed previously, we fail the installation, updater should handle
  those cases.

Bug: 306638108, 333034541
Change-Id: I0c4f567a4659596d3f43a4809cb4492beab35366
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5952412
Auto-Submit: Dominik Bylica <bylica@google.com>
Commit-Queue: Luke Klimek <zgroza@chromium.org>
Reviewed-by: Luke Klimek <zgroza@chromium.org>
Reviewed-by: Andrew Rayskiy <greengrape@google.com>
Cr-Commit-Position: refs/heads/main@{#1372651}