core: move genesis alloc types to core/types

[s1na]

This is in preparation for a pending refactor of the #27629. It is backwards-compatible.

[holiman]

LGTM, but funny that you mention "it's backwards-compatible" -- since it moves a publically exported type to a different package, it obviously cannot be fully backwards compatible. But I think it's fine with a little bit of fallout :)

[fjl]

It is fully backwards-compatible because of the type alias type GenesisAlloc = types.GenesisAlloc. Anywhere new type is used, you can still also use the old name. But it will show you a deprecation warning in the IDE.

[fjl]

External code will not be affected by this move. But we decided to change all of our internal uses of the type as well.