Introduce a specialize instruction for Array#pack

Instructions for this code:

```ruby
  # frozen_string_literal: true

[a].pack("C")
```

Before this commit:

```
== disasm: #<ISeq:<main>@test.rb:1 (1,0)-(3,13)>
0000 putself                                                          (   3)[Li]
0001 opt_send_without_block                 <calldata!mid:a, argc:0, FCALL|VCALL|ARGS_SIMPLE>
0003 newarray                               1
0005 putobject                              "C"
0007 opt_send_without_block                 <calldata!mid:pack, argc:1, ARGS_SIMPLE>
0009 leave
```

After this commit:

```
== disasm: #<ISeq:<main>@test.rb:1 (1,0)-(3,13)>
0000 putself                                                          (   3)[Li]
0001 opt_send_without_block                 <calldata!mid:a, argc:0, FCALL|VCALL|ARGS_SIMPLE>
0003 putobject                              "C"
0005 opt_newarray_send                      2, :pack
0008 leave
```

Co-authored-by: Maxime Chevalier-Boisvert <[email protected]>
Co-authored-by: Aaron Patterson <[email protected]>

1 files changed, 1 insertions, 0 deletions

diff --git a/vm.c b/vm.c
index 7e39940017..550ded3209 100644
--- a/vm.c
+++ b/vm.c
@@ -2278,6 +2278,7 @@ vm_redefinition_bop_for_id(ID mid)
     OP(NilP, NIL_P);
     OP(Cmp, CMP);
     OP(Default, DEFAULT);
+    OP(Pack, PACK);
 #undef OP
     }
     return -1;