* aarch64: Use smaller instruction helpers in ISLE
This commit moves the aarch64 backend's ISLE to be more similar to the
x64 backend's ISLE where one-liner instruction builders are used for
various forms of instructions instead of always using the
constructor-per-variant-of-`Inst`. Overall I think this change worked
out quite well and sets up some naming idioms as well for various forms
of instructions.
* rebase conflict
546e901d32