Update our browser design files, icon library and source new style guides

As of Firefox 89, our internal design files, main reference guide for Photon (design.firefox.com/photon) and Firefox's icon library (design.firefox.com/icons) are obsolete.

In order to support the transition onto the Firefox 91 ESR as best we can, the UX team will need access to:

• Updated design files/libraries for Figma (preferred, but not essential) or Sketch
• An updated pattern library/style guide or other reference material (if not included in the above)
• The new icon suite in vector format

It would also be great (although not critical) if we could discuss some way to stay in sync with any changes to the above too.