Basic strings

[vezenovm]

Related issue(s)

Resolves #383

The issue linked is to add log statements. Although not directly related, strings are being added to ultimately enable logging.

Description

This PR adds a basic string implementation. To correctly resolve string size we follow the same resolution strategy as arrays and under the hood we utilize Rust's String type and convert to a list of u8 integers.

Summary of changes

I added a String type to various type enums such as InputValue, UnresolvedType, Type in the HIR, Literal in the monomorphisation AST, etc. Strings are allowed to be passed into the ABI and compared against each other.

However, in this current implementation strings do not fully mock the functionality of arrays. This means we cannot replace individual elements of arrays, but a mutable string is possible by replacing the entire string value.

I debated whether or not to implement a string type directly or rather create a char type and then enable arrays to handle this char type. This felt like it would be a little bit more complex as we would then have to extend arrays to support string literals, and char literals would have to be added as well. To start, I went with a separate string type as it seems highly unlikely that many people are going to be doing string manipulation in Noir and the main goal of adding strings was to enable logging which will just require string literals. I could make this change right now, or I could open an issue for later to add chars and enable formatting/manipulation of strings.

Dependency additions / changes

(If applicable.)

Test additions / changes

I added a basic test checking whether or not we can pass string data to the ABI and compare it against string literals inside of Noir.

Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt with default settings.
• I have linked this PR to the issue(s) that it resolves.
• I have reviewed the changes on GitHub, line by line.
• I have ensured all changes are covered in the description.

Additional context

(If applicable.)

[jfecher]

Looks good. I take it it is currently blocked until #620 is merged

[jfecher]

Looks good, just some minor cleanup with removing unneeded comments then we can merge

[jfecher]

LGTM