Remove parser restriction on varargs positioning

crates/parser/test_data/parser/inline/ok/0123_param_list_vararg.rast

@@ -34,6 +34,18 @@ SOURCE_FILE
           WHITESPACE " "
           PARAM
             DOT3 "..."
+          COMMA ","
+          WHITESPACE " "
+          PARAM
+            WILDCARD_PAT
+              UNDERSCORE "_"
+            COLON ":"
+            WHITESPACE " "
+            PATH_TYPE
+              PATH
+                PATH_SEGMENT
+                  NAME_REF
+                    IDENT "u8"
           R_PAREN ")"
         WHITESPACE " "
         RET_TYPE

crates/parser/test_data/parser/inline/ok/0123_param_list_vararg.rs

@@ -1 +1 @@
-extern "C" { fn printf(format: *const i8, ...) -> i32; }
+extern "C" { fn printf(format: *const i8, ..., _: u8) -> i32; }

crates/parser/test_data/parser/inline/ok/0156_fn_def_param.rast

@@ -6,6 +6,10 @@ SOURCE_FILE
       IDENT "foo"
     PARAM_LIST
       L_PAREN "("
+      PARAM
+        DOT3 "..."
+      COMMA ","
+      WHITESPACE " "
       PARAM
         TUPLE_PAT
           L_PAREN "("

crates/parser/test_data/parser/inline/ok/0156_fn_def_param.rs

@@ -1 +1 @@
-fn foo((x, y): (i32, i32)) {}
+fn foo(..., (x, y): (i32, i32)) {}