feat(stdlib): Implement str as_bytes and into_bytes function

[Ethan-000]

Description

Problem*

Resolves #2138

Summary*

use dep::std;
fn main() {
    let a = "hello";
    let b = a.as_bytes();
    assert(b[0]==104);
    assert(b[1]==101);
    assert(b[2]==108);
    assert(b[3]==108);
    assert(b[4]==111);
    let mut c = a.into_bytes();
    assert(c.get(0)==104);
    assert(c.get(1)==101);
    assert(c.get(2)==108);
    assert(c.get(3)==108);
    assert(c.get(4)==111);
}

Documentation

• This PR requires documentation updates when merged.

  • I will submit a noir-lang/docs PR.
  • I will request for and support Dev Rel's help in documenting this PR.

Additional Context

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[vezenovm]

Once @jfecher comments are resolved this looks good

[tsujp]

The documentation in the release notes, PR title, and PR body here are incorrect. There is no method into_bytes(); rather there is as_bytes() and as_bytes_vec().

https://github.com/noir-lang/noir/blob/92549d432470244ff7e8581fbe02c744c88942d9/noir_stdlib/src/string.nr

[Ethan-000]

ah forgot to change the pr title after renaming the function