Prepare for SP-addressed locals

* libguile/vm-engine.c: Renumber opcodes, and take the opportunity to
  fold recent additions into more logical places.  Be more precise when
  describing the encoding of operands, to shuffle local references only
  and not constants, immediates, or other such values.
  (SP_REF, SP_SET): New helpers.
  (BR_BINARY, BR_ARITHMETIC): Take full 24-bit operands.  Our shuffle
  strategy is to emit push when needed to bring far locals near, then
  pop afterwards, shuffling away far destination values as needed; but
  that doesn't work for conditionals, unless we introduce a trampoline.
  Let's just do the simple thing for now.  Native compilation will use
  condition codes.
  (push, pop, drop): Back from the dead!  We'll only use these for
  temporary shuffling though, when an opcode can't address the full
  24-bit range.
  (long-fmov): New instruction, like long-mov but relative to the frame
  pointer.
  (load-typed-array, make-array): Don't use a compressed encoding so
  that we can avoid the shuffling case.  It would be a pain, given that
  they have so many operands already.

* module/language/bytecode.scm (compute-instruction-arity): Update for
  new instrution word encodings.

* module/system/vm/assembler.scm: Update to expose some opcodes
  directly, without the need for shuffling wrappers.  Adapt to
  instruction word encodings change.

* module/system/vm/disassembler.scm (disassembler): Adapt to instruction
  coding change.

module/language/bytecode.scm

@@ -34,34 +34,40 @@
 (define (compute-instruction-arity name args)
   (define (first-word-arity word)
     (case word
-      ((U8_X24) 0)
-      ((U8_U24) 1)
-      ((U8_L24) 1)
-      ((U8_U8_I16) 2)
-      ((U8_U12_U12) 2)
-      ((U8_U8_U8_U8) 3)))
+      ((X32) 0)
+      ((X8_S24) 1)
+      ((X8_F24) 1)
+      ((X8_C24) 1)
+      ((X8_L24) 1)
+      ((X8_S8_I16) 2)
+      ((X8_S12_S12) 2)
+      ((X8_S12_C12) 2)
+      ((X8_C12_C12) 2)
+      ((X8_F12_F12) 2)
+      ((X8_S8_S8_S8) 3)
+      ((X8_S8_S8_C8) 3)
+      ((X8_S8_C8_S8) 3)))
   (define (tail-word-arity word)
     (case word
-      ((U8_U24) 2)
-      ((U8_L24) 2)
-      ((U8_U8_I16) 3)
-      ((U8_U12_U12) 3)
-      ((U8_U8_U8_U8) 4)
-      ((U32) 1)
+      ((C32) 1)
       ((I32) 1)
       ((A32) 1)
       ((B32) 0)
       ((N32) 1)
-      ((S32) 1)
+      ((R32) 1)
       ((L32) 1)
       ((LO32) 1)
-      ((X8_U24) 1)
-      ((X8_U12_U12) 2)
-      ((X8_L24) 1)
+      ((C8_C24) 2)
+      ((B1_C7_L24) 3)
+      ((B1_X7_S24) 2)
+      ((B1_X7_F24) 2)
+      ((B1_X7_C24) 2)
       ((B1_X7_L24) 2)
-      ((B1_U7_L24) 3)
       ((B1_X31) 1)
-      ((B1_X7_U24) 2)))
+      ((X8_S24) 1)
+      ((X8_F24) 1)
+      ((X8_C24) 1)
+      ((X8_L24) 1)))
   (match args
     ((arg0 . args)
      (fold (lambda (arg arity)