Disallow WebView provider packages lower version than Chrome Stable

Doing so has security benefits, making sure the device is at least as secure as
the MonoChrome Stable on the system image.

This is implemented as checking WebView provider package versionCode against the
default available, non-fallback WebView provider package. On GMS devices, this
is MonoChrome Stable. On AOSP devices, this is standalone WebView.

BUG: 27469181
Change-Id: Id5b68ee28401a24843421cfcc3755e63196ac0f9