Makes AccountInfo repr(C)

[brooksprumo]

Problem

Please see #29852.

Since AccountInfo does not contain any Vecs, we can move the fields around and add repr(C) to ensure its layout remains stable. (This assumes that the layouts for Rc,RefCell, and slice do not change, which is verified in the check_type_assumptions test.)

Summary of Changes

Add repr(C) to AccountInfo

[alessandrod]

LGTM! I think it'd be nice to also reorder the checks in check_type_assumptions()? It checks the right offsets with the old field definition order which is a bit confusing

[brooksprumo]

I think it'd be nice to also reorder the checks in check_type_assumptions()? It checks the right offsets with the old field definition order which is a bit confusing

Noted. I will address this in a subsequent PR.

[brooksprumo]

I think it'd be nice to also reorder the checks in check_type_assumptions()? It checks the right offsets with the old field definition order which is a bit confusing

Noted. I will address this in a subsequent PR.

#30143