Add missing type hint for Token constructor

mypy thinks that Token's __init__ is inherited from __str__(). That's
not wrong -- it's just irrelevant, because Token also implements
__new__(). Token's _effective_ constructor signature is determined by
its __new__() method, so that's what I have used in the type hint.

Not clear if 'value' is supposed to be Any, but that's what I need in
my application. And it works just fine!

lark-stubs/lexer.pyi

@@ -85,6 +85,9 @@ class Token(str):
     end_column: int
     end_pos: int
 
+    def __init__(self, type_: str, value: Any, pos_in_stream: int = None, line: int = None, column: int = None, end_line: int = None, end_column: int = None, end_pos: int = None):
+        ...
+
     def update(self, type_: Optional[str] = None, value: Optional[str] = None) -> Token:
         ...