[HTML5] Better fullscreen, canvas resizing.

Three canvas resize policies:
- `None`: Godot window settings are ignored.
- `Project`: Godot handles the canvas like a native app (resizing it
  when setting the window size).
- `Adaptive`: Canvas size will always adapt to browser window size.

Use `None` if you want to control the canvas size with custom JavaScript
code.

platform/javascript/js/libs/library_godot_os.js

@@ -91,11 +91,6 @@ const GodotConfig = {
 	godot_js_config_locale_get: function (p_ptr, p_ptr_max) {
 		GodotRuntime.stringToHeap(GodotConfig.locale, p_ptr, p_ptr_max);
 	},
-
-	godot_js_config_canvas_resize_policy_get__sig: 'i',
-	godot_js_config_canvas_resize_policy_get: function () {
-		return GodotConfig.canvas_resize_policy;
-	},
 };
 
 autoAddDeps(GodotConfig, '$GodotConfig');