bpo-38407: Add docstrings for typing.SupportsXXX classes. (GH-16644)

(cherry picked from commit 8252c52)

Co-authored-by: Serhiy Storchaka <[email protected]>

Author: miss-islington

Lib/typing.py

@@ -1513,6 +1513,7 @@ def new_user(user_class: Type[U]) -> U:
 
 @runtime_checkable
 class SupportsInt(Protocol):
+    """An ABC with one abstract method __int__."""
     __slots__ = ()
 
     @abstractmethod
@@ -1522,6 +1523,7 @@ def __int__(self) -> int:
 
 @runtime_checkable
 class SupportsFloat(Protocol):
+    """An ABC with one abstract method __float__."""
     __slots__ = ()
 
     @abstractmethod
@@ -1531,6 +1533,7 @@ def __float__(self) -> float:
 
 @runtime_checkable
 class SupportsComplex(Protocol):
+    """An ABC with one abstract method __complex__."""
     __slots__ = ()
 
     @abstractmethod
@@ -1540,6 +1543,7 @@ def __complex__(self) -> complex:
 
 @runtime_checkable
 class SupportsBytes(Protocol):
+    """An ABC with one abstract method __bytes__."""
     __slots__ = ()
 
     @abstractmethod
@@ -1549,6 +1553,7 @@ def __bytes__(self) -> bytes:
 
 @runtime_checkable
 class SupportsIndex(Protocol):
+    """An ABC with one abstract method __index__."""
     __slots__ = ()
 
     @abstractmethod
@@ -1558,6 +1563,7 @@ def __index__(self) -> int:
 
 @runtime_checkable
 class SupportsAbs(Protocol[T_co]):
+    """An ABC with one abstract method __abs__ that is covariant in its return type."""
     __slots__ = ()
 
     @abstractmethod
@@ -1567,6 +1573,7 @@ def __abs__(self) -> T_co:
 
 @runtime_checkable
 class SupportsRound(Protocol[T_co]):
+    """An ABC with one abstract method __round__ that is covariant in its return type."""
     __slots__ = ()
 
     @abstractmethod