Replace TypeSignature::String with TypeSignature::Coercible

[jayzhan211]

Is your feature request related to a problem or challenge?

After #14440, we can use Coercible signature for existing String

                    TypeSignature::Coercible(vec![
                        Coercion::new_exact(TypeSignatureClass::Native(logical_string())),
                    ]),

Describe the solution you'd like

No response

And deprecate TypeSignature::String

Describe alternatives you've considered

No response

Additional context

#14440
#13301

[zjregee]

take