Fixes #2022, do not resume on Android when surfaceChanged

If the app is in landscape mode and the user presses the power button, a pause
is followed immediately by a surfaceChanged event because the lock screen
is shown in portrait mode. This triggers a "false" resume.
So, we just pause and resume following the onWindowFocusChanged events.

Also, wait for SDL_APP_WILLENTERBACKGROUND and SDL_APP_DIDENTERBACKGROUND before
blocking the event pump.

Xcode-iOS/Demos/src/common.c

@@ -0,0 +1,36 @@
+/*
+ *  common.c
+ *  written by Holmes Futrell
+ *  use however you want
+ */
+
+#include "common.h"
+#include "SDL.h"
+#include <stdlib.h>
+
+/*
+    Produces a random int x, min <= x <= max
+    following a uniform distribution
+*/
+int
+randomInt(int min, int max)
+{
+    return min + rand() % (max - min + 1);
+}
+
+/*
+    Produces a random float x, min <= x <= max
+    following a uniform distribution
+ */
+float
+randomFloat(float min, float max)
+{
+    return rand() / (float) RAND_MAX *(max - min) + min;
+}
+
+void
+fatalError(const char *string)
+{
+    printf("%s: %s\n", string, SDL_GetError());
+    exit(1);
+}