ATProto: run full handle resolution for ATProto.handle property

[snarfed]

Right now, when we store an ATProto user, we grab their handle from their DID doc's alsoKnownAs and store it in the handle property. That's generally ok, but when someone creates a new account and moves an existing handle to that new account, the old DID doc still has the old handle in alsoKnownAs, so when Bridgy Fed looks up the ATProto user with that handle, eg for Webfinger, it sometimes gets the old DID.

#1201 is related, but not the root cause here. We need to change ATProto.handle to do full, bidirectional handle resolution. Sigh, ok.

[lucidillusions]

@snarfed would this also solve the issue #39 where the bridge fails if I rename the bridged (pixelfed) account on bsky?

(or is this a new thing, since now bsky will start reserving our original bsky handle when we do custom domain - so it resolves that?)

[snarfed]

@lucidillusions you mean, if you change your Bluesky handle? That's #1074, right? The status there is mostly that we're blocked on fediverse software handling username changes. This issue is largely unrelated afaict.