Identifier str conversions

[LesterEvSe]

It allows us to easily and ergonomically convert Identifiers to and from standard &str slices across the codebase without having to manually unwrap or expose the inner Arc.

NOTE: This will be needed for future imports.

[gerau]

I am not sure if that is even needed, because the same implementations already exist in the wrapped_string! macro:

• AsRef is the as_inner method.
• From<&str> is the from_str_unchecked method (it is lengthier name, but in ✨ Imports with namespacing, pub/use #216 it is used only in tests anyway).

[LesterEvSe]

Okay, I have checked the architecture again and these changes can be removed