Supporting additional WebView implementations.

[lss4]

Consider this a follow-up of #2239.

As Bromite hasn't been updated for a while I've migrated to Mulch which is still being maintained.

Similar to Bromite, an overlay is needed to allow Mulch WebView to be used. However, the previous overlay (/system/product/overlay/treble-overlay-highpriomisc.apk) introduced in v411 (which added Bromite) is taking precedence, preventing other overlays from taking effect.

I've inspected the GSI mentioned in my issue (which is maintained by ponces) and confirmed the presence of the overlay in question... so for now, in order to use Mulch WebView in GSIs, one either needs to remove/mask the treble-overlay-highpriomisc.apk overlay or merge the entry for Mulch into it.

[phhusson]

I see. That's rather annoying, because this overlays exists for a reason: some OEMs set their own value of webviews in a vendor overlay, hence we need to overwrite it with a high priority overlay.

I welcome any suggestion.
I'm perfectly fine with allowlisting (with signing public key) all major webviews (I personnaly use mulch webview in my personal builds already).