40162: Build Fenix instrumented tests apk

Closes #40162 (closed).

I'm basing this on the branch from !165 (closed).

Currently, this builds *androidTest.apk for all build variants. I'm not sure if that's the best, or we should only do this for the nightlies.

This also needs a fenix branch with the fenix@238126dc fixup, otherwise there is a build error. The patch for fenix@623da161 is not needed to build successfully I believe, but if it's not there the androidTest.apk will always be the debug one.

I fetched the gradle deps, but okio-2.8.0 did not appear in the list as a result of that (not sure exactly why), so I added it manually.