add io.TextIOWrapper.read in 3.3 (#2248)

This is needed to make TextIOWrapper and a few classes that inherit
from it concrete in 3.3. I am actually not sure whether this method
exists at runtime; there's nothing in
https://docs.python.org/3/library/io.html#io.TextIOWrapper
that suggests it was added in 3.4. In any case, it hardly matters
since 3.3 usage should be very rare now.

stdlib/3/io.pyi

@@ -246,6 +246,7 @@ class TextIOWrapper(TextIO):
         def read(self, size: Optional[int] = ...) -> str: ...
     elif sys.version_info >= (3, 2):
         def readline(self, limit: int = ...) -> str: ...
+        def read(self, size: Optional[int] = ...) -> str: ...
     else:
         def readline(self) -> str: ...
     if sys.version_info >= (3, 2):