feat: add fmtstr::quoted_contents

[asterite]

Description

Problem

Resolves #5899
Resolves #5914

Summary

Two things here:

1. When interpolating quotes values inside a format string, we do that without producing the quote { and } parts, which is likely what a user would expect (similar to unquoting those values).
2. In order to create identifiers (or any piece of code in general) by joining severa quoted values you can use format strings together with the new fmtstr::contents method, which returns a Quoted value with the string contents (that is, without the leading and trailing double quotes).

Additional Context

I originally thought about a method like fmtstr::as_identifier that would try to parse the string contents as an identifier (maybe an Ident, or maybe a Path), returning Option<Quoted> and None in case it couldn't be parsed to that. But I think in general it could be more useful to just get the string contents as a Quoted value. After all, if it isn't an identifier you'll learn it later on once the value is unquoted or interpolated.

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]

Changes to Brillig bytecode sizes

Generated at commit: fca865cc6ea44ef8eae80608164f39632f7d73a2, compared to commit: 34f21c0eadfc8a03f5177d72de7958903de8ac98

There are no changes in circuit sizes

[github-actions]

🚀 Deployed on https://66d8c5ac7698c3368447f0ac--noir-docs.netlify.app

[github-actions]

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