Android: Segmentation fault fix, PendingIntent flag, and other fixes (#12960)

Android: Segmentation fault fix, PendingIntent flag, and other fixes (#12960)

* Android: Segmentation fault fix, PendingIntent flag, and other fixes

- Information about the crosshair is sent after camera initialization.
- Since API 31, PendingIntent requires mutability flag.
- super (class) is called in onRequestPermissionsResult().
- GameActivity suppresses "unused" warning since most of its methods are called from native code.
- Non-null safety is added for nullable function calls.
- Warning/error logging is added for various function calls' return value.

* Move utility functions into Utils.java

- Some nullable functions are changed to be non-null functions.
- Some null checking outside it is removed.
- More annotations are added to functions and parameters.