mesa: Make the android_stub be a set of non-installed shared libraries.

Previously, we included the stubs in our driver binaries, so they didn't call the actual system libraries for these functions. This was enough to build-test the Android code in CI without even the NDK.

To make NDK-built Mesa drivers useful, we need to link against these system libraries that aren't present in the NDK. Split the symbols to separate non-installed shared libraries and link against those, so that when you drop the resulting .so in your /vendor/lib64/hw/, it just works out.