[rcore_android] Allow setting window size on Android.

[StupidRepo]

My situation

1. User rotates device while app is open.
2. Android sends APP_CMD_CONFIG_CHANGED.
3. Resizing the framebuffer and setting screen sizes to reflect the new 'window size' causes stretching due to Android-reported width and height still (usually - see below) reporting with values from before the orientation change.

Why not just add this in AndroidCommandCallback's APP_CMD_CONFIG_CHANGED case?

Android does not send the correct width and height in time, therefore leading to you having to manually switch the height and width. This is fine, until you notice that Android has a somewhat-common chance to send the correct width and height and then everything gets stretched because you swapped the width to be the height to account for the wrong timing.

You could make a variable to mark the window as dirty then in a place that is triggered every frame, if that variable is true and the Android-reported size != current window size, set the variable to false and then update to the new size.

The solution for devs using raylib

1. Allow SetWindowSize to be usable, via this patch, on android.
2. Devs can now use the NDK themselves to check every frame if a resize occured:

extern struct android_app* GetAndroidApp();

static int ndk_window_width() {
	struct android_app* app = GetAndroidApp();
	if (!app || !app->window) return 0;

    return ANativeWindow_getWidth(app->window);
}
static int ndk_window_height() {
    struct android_app* app = GetAndroidApp();
    if (!app || !app->window) return 0;

    return ANativeWindow_getHeight(app->window);
}

3. Devs call these every frame, and do manual resize checking. If a resize is detected, call SetWindowSize(int width, int height).

Additional comments

Let me know if this is okay - personally I wouldn't accept this PR as I'm sure there is a solution that allows putting this code in APP_CMD_CONFIG_CHANGED while receiving correct sizes from Android (see my 'Why not ...' above for why we can't do this already).

This also is a better solution as it also correctly sets the size when INIT_WINDOW happens. So, if the app is in landscape and the users turns off the phone screen then turns it back on with the orientation in portrait, then that is also handled as the size change is detected.

Demos

Fix from this PR:

fixed.by.this.pr.mp4

Default behaviour:

app.stretch.mp4