Add lsh, rsh instructions

* libguile/vm-engine.c (lsh, rsh, lsh/immediate, rsh/immediate): New
  instructions taking unboxed bit counts.
* module/language/cps/compile-bytecode.scm (compile-function):
* module/language/cps/effects-analysis.scm:
* module/language/cps/specialize-numbers.scm (specialize-f64-unop):
  (specialize-u64-unop): Add ability to specialize add/immediate, etc,
  and add lsh/immediate as well.
  (specialize-u64-binop, specialize-u64-shift): Move rsh/lsh
  specialization to its own procedure, given that the bit count is
  already unboxed.
  (specialize-operations): Adapt to support more /immediate
  instructions.
* module/language/cps/type-fold.scm (mul): Reify an lsh/immediate
  instead of an ash.
* module/language/cps/types.scm (compute-ash-range): Add type inferrers
  for lsh, rsh, and their immediate variants.
* module/system/vm/assembler.scm: Export emit-lsh and so on.
* module/language/tree-il/compile-cps.scm (convert): Convert "ash" on
  immediates to rsh/immediate or lsh/immediate.

module/system/vm/assembler.scm

@@ -189,6 +189,10 @@
             emit-rem
             emit-mod
             emit-ash
+            emit-lsh
+            emit-rsh
+            emit-lsh/immediate
+            emit-rsh/immediate
             emit-fadd
             emit-fsub
             emit-fmul