impl Iden for String (#1019)

An obvious and often-requested feature.

Turns out, now I need this for my other PRs:

- #1020
- There's another stacked PR in progress, I'll link it soon

Author: Expurple

src/types/iden/core.rs

@@ -51,6 +51,16 @@ impl Iden for &'static str {
     }
 }
 
+impl Iden for String {
+    fn quoted(&self) -> Cow<'static, str> {
+        Cow::Owned(self.clone())
+    }
+
+    fn unquoted(&self) -> &str {
+        self
+    }
+}
+
 #[cfg(feature = "thread-safe")]
 /// Identifier statically known at compile-time.
 pub trait IdenStatic: Iden + Copy + Send + Sync + 'static {
@@ -98,12 +108,6 @@ where
     }
 }
 
-impl From<String> for DynIden {
-    fn from(value: String) -> Self {
-        DynIden(Cow::Owned(value))
-    }
-}
-
 impl<T> From<T> for DynIden
 where
     T: Iden,