WGSL front end: Only accept ASCII chars in identifiers

Previously the lexer would accept any alphanumeric character as part of an
identifier. The spec only allowes identifiers to consist of ASCII alphanumeric
characters though.

src/front/wgsl.rs

@@ -89,7 +89,7 @@ mod lex {
                 (Token::Number(number), rest)
             }
             'a'..='z' | 'A'..='Z' | '_' => {
-                let (word, rest) = consume_any(input, |c| c.is_alphanumeric() || c == '_');
+                let (word, rest) = consume_any(input, |c| c.is_ascii_alphanumeric() || c == '_');
                 (Token::Word(word), rest)
             }
             '"' => {