Add PrimCallConv support to GHCi

This adds support for calling Cmm code from bytecode using the native
calling convention, allowing modules that use `foreign import prim`
to be loaded and debugged in GHCi.

This patch introduces a new `PRIMCALL` bytecode instruction and
a helper stack frame `stg_primcall`. The code is based on the
existing functionality for dealing with unboxed tuples in bytecode,
which has been generalised to handle arbitrary calls.

Fixes #22051