Account selector improvements and minor fixes

[hjiangsu]

Pull Request Description

This PR adds the following changes/fixes:

• Fixes an issue where long pressing on the account option on the bottom navigation bar would often times show the tooltip instead of the account selector
• Fixes a minor visual bug where the drag handle of the account selector was mismatched
• Refactors the account selector modal to use slivers, and moved add account/instance to the top

Let me know what you think of the changes!

Issue Being Fixed

Issue Number: N/A

Screenshots / Recordings

Checklist

• Did you update CHANGELOG.md?
• Did you use localized strings where applicable?
• Did you add semanticLabels where applicable for accessibility?

[micahmo]

LGTM!

My only concern is that the "add anonymous account" button might not be obvious and people might miss that the feature exists. Maybe in the future, we can have a single button, and within the account creation dialog, we can have an option to switch it to anonymous, which will just hide the user fields.

[hjiangsu]

My only concern is that the "add anonymous account" button might not be obvious and people might miss that the feature exists. Maybe in the future, we can have a single button, and within the account creation dialog, we can have an option to switch it to anonymous, which will just hide the user fields.

I tried to look for some more distinguishable icons for the anonymous accounts, but was unable to find any that suited. I do think your idea of having this in the account creation dialog makes sense! I'll merge this in and we can think about implementing this.