OP_AELEMFASTLEX_STORE - combined sassign/aelemfast_lex

This commit introduces a new OP to replace simple cases of OP_SASSIGN
and OP_AELEMFAST_LEX. (Similar concept to GH Perl#19943)

For example, `my @ary; $ary[0] = "boo"` is currently implemented as:
    7     <2> sassign vKS/2 ->8
    5        <$> const[PV "boo"] s ->6
    -        <1> ex-aelem sKRM*/2 ->7
    6           <0> aelemfast_lex[@ary:1,2] sRM ->7
    -           <0> ex-const s ->-

But now will be turned into:
    6     <1> aelemfastlex_store[@ary:1,2] vKS ->7
    5        <$> const(PV "boo") s ->6
    -        <1> ex-aelem sKRM*/2 ->6
    -           <0> ex-aelemfast_lex sRM ->6
    -           <0> ex-const s ->-

This is intended to be a transparent performance optimization.
It should be applicable for RHS optrees of varying complexity.

ext/Opcode/Opcode.pm

@@ -305,7 +305,7 @@ invert_opset function.
     rv2sv sassign padsv_store
 
     rv2av aassign aelem aelemfast aelemfast_lex aslice kvaslice
-    av2arylen
+    av2arylen aelemfastlex_store
 
     rv2hv helem hslice kvhslice each values keys exists delete
     aeach akeys avalues multideref argelem argdefelem argcheck

lib/B/Deparse.pm

@@ -4305,6 +4305,17 @@ sub pp_gv {
     return $self->maybe_qualify("", $self->gv_name($gv));
 }
 
+sub pp_aelemfastlex_store {
+    my $self = shift;
+    my($op, $cx) = @_;
+    my $name = $self->padname($op->targ);
+    $name =~ s/^@/\$/;
+    my $i = $op->private;
+    $i -= 256 if $i > 127;
+    my $val = $self->deparse($op->first, 7);
+    return $self->maybe_parens("${name}[$i] = $val", $cx, 7);
+}
+
 sub pp_aelemfast_lex {
     my $self = shift;
     my($op, $cx) = @_;