a/android: Only look up the standardized intent to find our own package.

Should allow a constrained query manifest in client apps.

I still need to do the standardization/spec stuff to actually specify that this is how we're gonna solve the problem, but I think this solves the problem with target SDKs above 29. I think it can be merged, since it doesn't keep things from working if it's unneeded, it just takes a slightly more roundabout path.