AK: Remove ByteString from GenericLexer

A bunch of users used consume_specific with a constant ByteString
literal, which can be replaced by an allocation-free StringView literal.

The generic consume_while overload gains a requires clause so that
consume_specific("abc") causes a more understandable and actionable
error.

Meta/Lagom/Tools/CodeGenerators/LibWeb/GenerateWindowOrWorkerInterfaces.cpp

@@ -28,7 +28,7 @@ static void consume_whitespace(GenericLexer& lexer)
     while (consumed) {
         consumed = lexer.consume_while(is_ascii_space).length() > 0;
 
-        if (lexer.consume_specific("//")) {
+        if (lexer.consume_specific("//"sv)) {
             lexer.consume_until('\n');
             lexer.ignore();
             consumed = true;