Pass whether a Regexp is a /.../ literal from mruby codegen to Artichoke

[lopopolo]

With these changes:

$ cargo run --bin airb -q
artichoke 0.1.0-pre.0 (2022-08-11 revision 6046) [x86_64-apple-darwin]
[rustc 1.63.0 (4b91a6ea7 2022-08-08) on x86_64-apple-darwin]
>>> /airb/in

[artichoke-backend/src/extn/core/regexp/enc.rs:13] encoding = [
    110,
]
[artichoke-backend/src/extn/core/regexp/opts.rs:18] options = [
    105,
    108,
]
[artichoke-backend/src/extn/core/regexp/trampoline.rs:22] options = Some(
    Options {
        flags: IGNORECASE | LITERAL,
    },
)
=> /airb/in

And the exceptions:

$ cargo run --bin airb -q
artichoke 0.1.0-pre.0 (2022-08-11 revision 6046) [x86_64-apple-darwin]
[rustc 1.63.0 (4b91a6ea7 2022-08-08) on x86_64-apple-darwin]
>>> /abc/in
=> /abc/in
>>> /abc/in.send(:initialize, "xyz")
Traceback (most recent call last):
        2: from (airb):2
        1: from (airb):2:in initialize
SecurityError (can't modify literal regexp)
>>> Regexp.compile('jkl')
=> /jkl/
>>> Regexp.compile('jkl').send(:initialize, "qwerty")
Traceback (most recent call last):
        2: from (airb):4
        1: from (airb):4:in initialize
TypeError (already initialized regexp)

[lopopolo]

This is blocking:

• Fix Regexp#initialize to raise FrozenError instead of FrozenError on reinitializing literal Regexp in Ruby 3 #2081

[lopopolo]

Tracking the upstreaming to artichoke/mruby the parser and codegen changes from aab134d here:

• Take changes to Regexp parsing from Artichoke mruby#20