Misc verification dialog UI improvements

[duxovni]

While reviewing matrix-org/matrix-react-sdk#6811, Amsha and I discussed several design issues with the cross-signing flow that predated my changes and were beyond the scope of issues #18536 and #17765. In the interest of getting the improved functionality merged sooner, I'm leaving those changes out of the PR, and spinning them off into a new issue just so we don't lose track of them. I might split these into individual issues later on.

• Try to keep the dialog box the same size across the various stages of verification
• Instead of popping up even more dialogs for things like secret storage access, interactive auth, etc, see if we can integrate those into the verification modal
• The "they match"/"they don't match" buttons on the emoji comparison dialog use an outdated button style, update those to match the overall Element UI
• The flow for verifying from another device has some redundant headers/sub-headers that should be removed
• On the interactive auth dialog that shows up while resetting cross-signing keys, if we're using password authentication, consider adding the username above the password prompt to make clear that we need the user's login password (as opposed to, say, the verification key that we just made them create)
• If we're verifying using the recovery key/phrase, it's awkward to only prompt for the recovery phrase and have a separate link to click if you want to use the recovery key instead. Ideally this would just be a single textbox that can take either a passphrase or a key and figure out which one it is, alongside a button for uploading a key instead. (As an even broader change, it might be nice to do away with this distinction altogether, and only give the user a correct-horse-battery-staple type passphrase when they set up secret storage, but that's a topic for more in-depth discussion.)
• Don't include "reset all" link in the Access Secret Storage dialog in this context

[duxovni]

Currently splitting this into individual issues for easier tracking, I'll close this once that's done