chore: Add a helper function fmtstr::as_quoted_str

[jfecher]

Description

Problem*

Resolves #9274 (comment)

Summary*

Adds a helper function to make this behavior more discoverable for users.

Additional Context

as_quoted_str is not actually required here since lowering a format string will lower it into a normal string, per the example in the metaprogramming docs:

fn main() {
    let foo = comptime {
        let i = 2;
        f"i = {i}"
    };
    assert_eq(foo, "i = 2");
}

But adding the method makes this behavior easier to find for users and removes the need for an extra comptime block sometimes.

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

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

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Test Suite Duration'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 91a9133	Previous: d2a51b6	Ratio
test_report_AztecProtocol_aztec-packages_noir-projects_aztec-nr	5 s	4 s	1.25
test_report_AztecProtocol_aztec-packages_noir-projects_noir-protocol-circuits_crates_blob	4 s	3 s	1.33
test_report_AztecProtocol_aztec-packages_noir-projects_noir-protocol-circuits_crates_reset-kernel-lib	2 s	1 s	2
test_report_AztecProtocol_aztec-packages_noir-projects_noir-protocol-circuits_crates_types	2 s	1 s	2

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench

[github-actions]

🚀 Deployed on https://6880f612c98ed800b75b3d09--noir-docs.netlify.app

[github-actions]

FYI @noir-lang/developerrelations on Noir doc changes.

[asterite]

Nice!