Replaces type aliases of raw integral types with the more type-safe Imm
template, like how the AArch64 frontend has been using it.
This makes the two frontends more consistent with one another.
Performs a similar tidying up of the Thumb translator, like what was
done with the regular ARM translator to make it consistent with the rest
of the codebase.
The A32 backend (both Thumb and ARM), will likely see more changes to it
in the near future, so this just acts as a "dusting off".
