token-2022: Support extensions in InitializeAccount variations

[CriesofCarrots]

InitializeAccount variations should initialize extensions required by the mint.
This PR adds that support.

Base and native mint cases are covered by existing test suite. The extended-mint cases still need testing, but I wanted to PR this now because: (a) that testing will be a lot easier when InitializeMint implementations for extensions are done; and (b) I wanted to see what you think of StateWithExtensionsMut::init_extension_from_type() and the error-type change in StateWithExtensionsMut::unpack_uninitialized() now. Thoughts?

[joncinque]

Looking good! Just a few comments and questions, but for the most part this is great

[CriesofCarrots]

@joncinque , I think this is ready for another look.
To come separately:

• A bunch of processor.rs and ProgramTest tests, when token: Add extension support in mint init #2744 is in
• A PR removing the AlreadyInitialized check (and reverting the comment changes), for discussion

[joncinque]

Really really close, just two last little questions

[joncinque]

Thanks for the changes, looks good!