feat: implement str_as_bytes in the comptime interpreter (#5887)

# Description

## Problem\*

Resolves <!-- Link to GitHub Issue -->

## Summary\*

This PR implements converting a string to a byte array in comptime,
something very useful for function signatures in aztec-nr

## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

compiler/noirc_frontend/src/hir/comptime/interpreter/builtin.rs

@@ -126,6 +126,7 @@ impl<'local, 'context> Interpreter<'local, 'context> {
             "slice_push_back" => slice_push_back(interner, arguments, location),
             "slice_push_front" => slice_push_front(interner, arguments, location),
             "slice_remove" => slice_remove(interner, arguments, location, call_stack),
+            "str_as_bytes" => str_as_bytes(interner, arguments, location),
             "struct_def_as_type" => struct_def_as_type(interner, arguments, location),
             "struct_def_fields" => struct_def_fields(interner, arguments, location),
             "struct_def_generics" => struct_def_generics(interner, arguments, location),
@@ -242,6 +243,32 @@ fn slice_push_back(
     Ok(Value::Slice(values, typ))
 }
 
+fn str_as_bytes(
+    interner: &NodeInterner,
+    arguments: Vec<(Value, Location)>,
+    location: Location,
+) -> IResult<Value> {
+    let (string, string_location) = check_one_argument(arguments, location)?;
+
+    match string {
+        Value::String(string) => {
+            let string_as_bytes = string.as_bytes();
+            let bytes_vector: Vec<Value> = string_as_bytes.iter().cloned().map(Value::U8).collect();
+            let byte_array_type = Type::Array(
+                Box::new(Type::Constant(string_as_bytes.len() as u32)),
+                Box::new(Type::Integer(Signedness::Unsigned, IntegerBitSize::Eight)),
+            );
+            Ok(Value::Array(bytes_vector.into(), byte_array_type))
+        }
+        value => {
+            let type_var = Box::new(interner.next_type_variable());
+            let expected = Type::Array(type_var.clone(), type_var);
+            let actual = value.get_type().into_owned();
+            Err(InterpreterError::TypeMismatch { expected, actual, location: string_location })
+        }
+    }
+}
+
 /// fn as_type(self) -> Type
 fn struct_def_as_type(
     interner: &NodeInterner,

test_programs/compile_success_empty/comptime_str_as_bytes/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "comptime_str_as_bytes"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.24.0"
+
+[dependencies]

test_programs/compile_success_empty/comptime_str_as_bytes/src/main.nr

@@ -0,0 +1,9 @@
+fn main() {
+    comptime
+    {
+        let hello_world_string = "hello world";
+        let hello_world_bytes: [u8; 11] = [0x68, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64];
+
+        assert_eq(hello_world_string.as_bytes(), hello_world_bytes);
+    }
+}