immersiveweb.dev updates

Hi Everyone,

I have added some more rows to the support table
<https://immersiveweb.dev/#supporttable>: hit-test, dom-overlays and layers.

If you work for a group implementing WebXR it would be great if you could
fill out any bits you can.

It's okay if you don't have plans yet or can't reveal them it's okay to
leave the cells blank.

You can edit the table here
<https://github.com/immersive-web/immersiveweb.dev/blob/master/_includes/compat-table.html>
or email me and I can update it,

Thank you,

Ada