create C API for getting screen size

Author: jakogut

src/library_browser.js

@@ -1373,6 +1373,14 @@ var LibraryBrowser = {
     Module['setWindowTitle'](UTF8ToString(title));
   },
 
+  emscripten_get_screen_size__proxy: 'sync',
+  emscripten_get_screen_size__sig: 'vii',
+  emscripten_get_screen_size: function(width, height) {
+    var screen = Module['screen'];
+    {{{ makeSetValue('width', '0', 'screen.width', 'i32') }}};
+    {{{ makeSetValue('height', '0', 'screen.height', 'i32') }}};
+  },
+
   emscripten_hide_mouse__proxy: 'sync',
   emscripten_hide_mouse__sig: 'v',
   emscripten_hide_mouse: function() {

system/include/emscripten/emscripten.h

@@ -136,6 +136,7 @@ extern void emscripten_force_exit(int status);
 double emscripten_get_device_pixel_ratio(void);
 
 void emscripten_set_window_title(char *);
+void emscripten_get_screen_size(int *width, int *height);
 void emscripten_hide_mouse(void);
 void emscripten_set_canvas_size(int width, int height) __attribute__((deprecated("This variant does not allow specifying the target canvas", "Use emscripten_set_canvas_element_size() instead")));
 void emscripten_get_canvas_size(int *width, int *height, int *isFullscreen) __attribute__((deprecated("This variant does not allow specifying the target canvas", "Use emscripten_get_canvas_element_size() and emscripten_get_fullscreen_status() instead")));