script: Add message to SyntaxError (#39056)

Adding an optional message to be attached to a SyntaxError. Unblocks
#39050.

The enum definition of Syntax is now `Syntax(Option<String>)`. Future
PRs should probably add more appropriate messages to some of the
`Syntax(None)`s.

Testing: Just a refactor
Fixes: Partially #39053

Signed-off-by: Ashwin Naren <arihant2math@gmail.com>

components/script/dom/idbdatabase.rs

@@ -212,7 +212,7 @@ impl IDBDatabaseMethods<crate::DomTypeHolder> for IDBDatabase {
         // Step 5
         if let Some(path) = key_path {
             if !is_valid_key_path(path) {
-                return Err(Error::Syntax);
+                return Err(Error::Syntax(None));
             }
         }