Recreate PWA app shims when app shim version changes.

In addition to recreating extensino based app shims, PWA app shims are
now also recreated. Also adds a unit test for said behavior.

Also fixes a bug in my previous CL where I moved the core updating logic
around, making sure that we persist the current version number in prefs
even if it matches what we read from prefs, as the default value being
equal to the current version would mean that otherwise we would always
read the current version from prefs and never update anything.

Bug: 1380711
Change-Id: I350a5159f2c651f3520acf93988c7497abec822b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4009479
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1068282}