Add parser stubs (#3822)

stdlib/2and3/parser.pyi

@@ -0,0 +1,29 @@
+from typing import Any, List, Sequence, Text, Tuple, Union
+from types import CodeType
+
+import sys
+
+if sys.version_info >= (3, 6):
+    from builtins import _PathLike
+    _Path = Union[str, bytes, _PathLike]
+else:
+    _Path = Union[str, bytes]
+
+def expr(source: Text) -> STType: ...
+def suite(source: Text) -> STType: ...
+def sequence2st(sequence: Sequence[Any]) -> STType: ...
+def tuple2st(sequence: Sequence[Any]) -> STType: ...
+def st2list(st: STType, line_info: bool = ..., col_info: bool = ...) -> List[Any]: ...
+def st2tuple(st: STType, line_info: bool = ..., col_info: bool = ...) -> Tuple[Any]: ...
+def compilest(st: STType, filename: _Path = ...) -> CodeType: ...
+def isexpr(st: STType) -> bool: ...
+def issuite(st: STType) -> bool: ...
+
+class ParserError(Exception): ...
+
+class STType:
+    def compile(self, filename: _Path) -> CodeType: ...
+    def isexpr(self) -> bool: ...
+    def issuite(self) -> bool: ...
+    def tolist(self, line_info: bool = ..., col_info: bool = ...) -> List[Any]: ...
+    def totuple(self, line_info: bool = ..., col_info: bool = ...) -> Tuple[Any]: ...