Add and update include guards

Include guards in most changed files were missing, I added them keeping
the same style as other SDL files. In some cases I moved the include
guards around to be the first thing the header has to take advantage of
any possible improvements compiler may have for inclusion guards.

Fixed bug 4335 - Android NDK build error

dmuratshin

LOCAL_SRC_FILES shouldn't use $(LOCAL_PATH)

Updated Android project files and documentation

This change looks okay in the general case.
If we run into problems where these events aren't dispatched (initialized on a different thread than the main thread?) we may need to create a separate thread to handle device notifications like we do with the windows joystick subsystem.

hidapi: Don't run a separate event loop for device notifications.

Fixes Bugzilla #4286.

Added patch note for SDL_GameControllerGetPlayerIndex() and friends

Don't build SDL_JOYSTICK_HIDAPI by default on iOS
If you enable this, you'll need to link with CoreBluetooth.framework and add something like this to your Info.plist:
<key>NSBluetoothPeripheralUsageDescription</key>
<string>MyApp would like to remain connected to nearby bluetooth Game Controllers and Game Pads even when you're not using the app.</string>

Generalized the XInput user index into a player index

Fixed initializing XInput user index

Added SDL_JoystickGetXInputUserIndex()