Include webxr layers polyfill.

TODO: Verify that this is a good place to link it to, or include it directly.

Now the web version works immersively, but no controllers.

Author: mgiuca

export_presets.cfg

@@ -96,7 +96,8 @@ vram_texture_compression/for_desktop=true
 vram_texture_compression/for_mobile=false
 html/export_icon=true
 html/custom_html_shell=""
-html/head_include=""
+html/head_include="<script src=\"https://cdn.jsdelivr.net/npm/webxr-layers-polyfill@latest/build/webxr-layers-polyfill.min.js\"></script>
+<script>var layersPolyfill = new WebXRLayersPolyfill();</script>"
 html/canvas_resize_policy=2
 html/focus_canvas_on_start=true
 html/experimental_virtual_keyboard=false