Could the Android NDK Resolver also check for ANDROID_HOME?

Since `ANDROID_HOME` is [one of most useful environment variables to set ](https://developer.android.com/tools/variables), it would be helpful if the resolver checked for it as well.

https://github.com/dart-lang/native/blob/e78967cc8ef3de2d4e283645c509658f39d9225d/pkgs/native_toolchain_c/lib/src/native_toolchain/android_ndk.dart#L38