This'll make it slightly nicer to do basic constant folding for 32-bit
and 64-bit variants of the same IR opcode type. By that, I mean it's
possible to inspect immediate values without a bunch of conditional
checks beforehand to verify that it's possible to call GetU32() or
GetU64, etc.
enum classes are still considered complete types when forward declared
(as the compiler knows the exact size of the type from the declaration
alone). The only difference in this case being that the members of the
enum class aren't visible. Given we don't use the members within this
header in any way, we can simply forward declare them here and remove
the inclusions.
ARM's Architecture Specification Language doesn't distinguish between floats and integers
as much as we do. This makes some things difficult to implement. Since our register
allocator is now capable of allocating values to XMMs and GPRs as necessary, the
Transfer IR instructions are no longer necessary as they used to be and they can be
removed.
