Audit each of our UX components for accessibilty issues

As discussed in our on-boarding, we have various new UX components added to Tor Browser. Accessibility concerns have historically not been a high priority. We should go through each of our components and ensure (at least on a technical level) that the proper annotations/etc are set in the XUL/HTML.

The list of features and their commit hashes in the tor-browser-102.2.0esr-12.0-2 branch:

• New Identity ( d627ac1c )
• Security Level/Slider ( 231b7a82 )
• New User Onboarding ( 5b6d65d6 )
• Letterboxing ( bb3ee4b7 )
• Crypto Safety ( b2f764ca )
• Profile Access Error Messages ( b924418a )
• External App Helper Dialog ( ba292b8b, but also in torbutton.git )
• about:preferences additions ( a245f127 )
• TorConnect captive portal/tor bootstrapping ( 777c84f5 )
• Tor Browser Updater ( 413ad7d4 )
• about:tbupdate changleog ( d15354ca )
• Onion Service specific URLbar icons+dialog changes ( a940145e )
• V3 Onion Service Auth prompt ( 422ba974 )
• Onion Location ( 46a0c98c )
• Integrated Tor Browser Manual ( 8e4a269d )
• Circuit Display Dropdown ( torbutton.git )
• about:tor page ( torbutton.git )
• about:rulesets ( f1b77124 ) ( thanks @pierov )

@pierov @duncan feel free to add to this list as I'm sure something's been forgotten

I will also send this ticket to some screen-reader users that have helped us in the past with testing for their input on nay known pain-points.