Create own gradle project

Right now the Gradle compiler is included in the android-toolchain project in different versions. It seems to change more often and differently for our mobile projects (above all application-services, android-components, and fenix) which is causing a toolchain rebuild and subsequent project rebuilding more often than actually needed (why should the rust project get rebuilt for all architectures just because the fenix compiler changed?).

I think we can solve this by having an own gradle project and depending at least the three above mentioned projects on it. We can use the pc(c("origin_project"), "var/$foo") trick to give the right compiler vesion back to the project as they vary widely at the moment.

That way we keep the flexibility for staying close to the actually used compiler versions by Mozilla's projects while only rebuilding the directly affected projects in case a Gradle version bump happened.