Since we are now able to build against GeckoView Nightly and GeckoView Beta,
we should create the GeckoRuntime from a flavor-specific source set.
Creating the runtime is not covered by the AC abstraction and so API changes
in GeckoView Nightly can break the build and leaves us with no option to fix
it from a shared code base. Separating the creation of GeckoRuntime
allows us to adapt individually and also to configure the runtimes
differently.
Previously, this passed through to HomeActivity, but Intent arguments
were dropped. That means that actions (`-a
android.intent.action.VIEW`) and URLs (`-d data:...`) were dropped,
which means that Gecko itself wasn't started (and wasn't started with
a session owned by Fenix itself).
This simply passes through the intent to its final destination.
Along the way, I also enabled remote debugging for these test
configurations; it's probably not necessary, but eventually I want all
automation to be controlled by that setting. See
[Bug 1524673](https://bugzilla.mozilla.org/show_bug.cgi?id=1524673)
for some of the motivation. This agrees with Chrome, and should
generalize to future remote control protocols.
Sebastian Kaspari