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/internal/basic_operators.h b/internal/basic_operators.h
index a59403631e..4732a65403 100644
--- a/internal/basic_operators.h
+++ b/internal/basic_operators.h
@@ -37,6 +37,7 @@ enum ruby_basic_operators {
     BOP_OR,
     BOP_CMP,
     BOP_DEFAULT,
+    BOP_PACK,
 
     BOP_LAST_
 };