script_bindings: Eliminate DOMString::from_string (#43089)

This method is the same as `DOMString::from` with a `String` argument
and `From` and `Into` are preferred when writing modern Rust.

Testing: This should not change behavior and is thus covered by existing
tests.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/css/csslayerstatementrule.rs

@@ -83,7 +83,7 @@ impl CSSLayerStatementRuleMethods<crate::DomTypeHolder> for CSSLayerStatementRul
             .borrow()
             .names
             .iter()
-            .map(|name| DOMString::from_string(name.to_css_string()))
+            .map(|name| name.to_css_string().into())
             .collect();
         to_frozen_array(names.as_slice(), cx, retval, can_gc)
     }