Improve fee payer txn submission APIs

[heliuchuan]

Description

This simplifies the fee payer APIs by reducing the steps needed to submit such a transaction while still maintaining support for remote signing.

Now the txn may be submitted either on the fee payer side or the sender side.

This also improves the keyless experience as proofs may be fetched asynchronously, in those cases since submission is an async function where we can await the proof fetch.

Test Plan

Tested via sponsored txn example.

More tests in progress

Related Links

[0xmaayan]

Have you seen this PR? following upcoming changes to the framework
#467

[heliuchuan]

Have you seen this PR? following upcoming changes to the framework #467

I have but is it relevant to this PR? doesn't seem so afaict

[GhostWalker562]

Looks good, seems to miss one condition though.

1. signAndSubmitTransaction -> sender: Account, feePayer: Account (1 step sign)
2. signAndSubmitTransaction -> sender: Account, feePayer: AccountAuthenticator (2 step sign)
3. signAndSubmitAsFeePayer -> sender: AccountAuthenticator, feePayer: Account (2 step sign)
4. (Missing) signAndSubmitAsFeePayer -> sender: Account, feePayer: Account (1 step sign)

[gregnazario]

KeylessAccountCommon seems like the wrong name for that interface, and it's a little weird of functionality here

[heliuchuan]

4. (Missing) signAndSubmitAsFeePayer -> sender: Account, feePayer: Account (1 step sign)

I figure that this doesn't make sense. If you are submitting as the fee payer you don't have access to the sender account and the sender ought to send you an authenticator that's valid for sponsorship.

Additionally the case is covered by the usual signAndSubmitTransaction.