Parse XPM without SDL_image

We encounter some problems with SDL2_image on MSYS2 (Windows), so
implement our own XPM parsing which does not depend on SDL_image.

The input XPM is considered safe (it's in our source repo), so do not
check XPM format errors. This implies that read_xpm() is not safe to
call on any unsafe input.

Although less straightforward, use SDL_CreateRGBSurfaceFrom() instead of
SDL_CreateRGBSurfaceWithFormatFrom() because it is available with SDL
versions older than 2.0.5.

app/meson.build

@@ -13,6 +13,7 @@ src = [
     'src/scrcpy.c',
     'src/server.c',
     'src/strutil.c',
+    'src/tinyxpm.c',
 ]
 
 if host_machine.system() == 'windows'
@@ -26,7 +27,6 @@ dependencies = [
     dependency('libavcodec'),
     dependency('libavutil'),
     dependency('sdl2'),
-    dependency('SDL2_image'),
     dependency('SDL2_net'),
 ]