WebView downgrade prevention logic

Prevent *any* WebView provider packages to be downgraded lower than MonoChrome
Stable on the system image.

Assuming that all (and future) WebView provider packages follow the same
versionCode scheme, we can compare the subsection of Chromium versionCode that
contains branch number, which is done by ignoring the least significant 5
digits.

Note this CL is a follow-up to go/ag/895502.

BUG: 27469181
Change-Id: Iffe3c4b7f912d48c034f107079e065e54130713f