fix: parsing of ? opt-out trait bounds

thanks to Veykril

crates/parser/src/grammar/generic_params.rs

@@ -133,6 +133,12 @@ fn type_bound(p: &mut Parser) -> bool {
     match p.current() {
         LIFETIME_IDENT => lifetime(p),
         T![for] => types::for_type(p, false),
+        T![?] if p.nth_at(1, T![for]) => {
+            // test question_for_type_trait_bound
+            // fn f<T>() where T: ?for<> Sized {}
+            p.bump_any();
+            types::for_type(p, false)
+        }
         current => {
             match current {
                 T![?] => p.bump_any(),

crates/parser/test_data/parser/inline/ok/0201_question_for_type_trait_bound.rast

@@ -0,0 +1,47 @@
+SOURCE_FILE
+  FN
+    FN_KW "fn"
+    WHITESPACE " "
+    NAME
+      IDENT "f"
+    GENERIC_PARAM_LIST
+      L_ANGLE "<"
+      TYPE_PARAM
+        NAME
+          IDENT "T"
+      R_ANGLE ">"
+    PARAM_LIST
+      L_PAREN "("
+      R_PAREN ")"
+    WHITESPACE " "
+    WHERE_CLAUSE
+      WHERE_KW "where"
+      WHITESPACE " "
+      WHERE_PRED
+        PATH_TYPE
+          PATH
+            PATH_SEGMENT
+              NAME_REF
+                IDENT "T"
+        COLON ":"
+        WHITESPACE " "
+        TYPE_BOUND_LIST
+          TYPE_BOUND
+            QUESTION "?"
+            FOR_TYPE
+              FOR_KW "for"
+              GENERIC_PARAM_LIST
+                L_ANGLE "<"
+                R_ANGLE ">"
+              WHITESPACE " "
+              PATH_TYPE
+                PATH
+                  PATH_SEGMENT
+                    NAME_REF
+                      IDENT "Sized"
+    WHITESPACE " "
+    BLOCK_EXPR
+      STMT_LIST
+        L_CURLY "{"
+        R_CURLY "}"
+  WHITESPACE "\n"

crates/parser/test_data/parser/inline/ok/0201_question_for_type_trait_bound.rs

@@ -0,0 +1 @@
+fn f<T>() where T: ?for<> Sized {}