[types] Make MethodType generic

[srittau]

No description provided.

[srittau]

Will be useful for #15977.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

pydantic (https://github.com/pydantic/pydantic)
- pydantic/experimental/arguments_schema.py:41: error: Argument 1 to "_arguments_schema" of "GenerateSchema" has incompatible type "Callable[..., Any]"; expected "FunctionType | MethodType | partial[Any]"  [arg-type]
+ pydantic/experimental/arguments_schema.py:41: error: Argument 1 to "_arguments_schema" of "GenerateSchema" has incompatible type "Callable[..., Any]"; expected "FunctionType | MethodType[[VarArg(Any), KwArg(Any)], Any] | partial[Any]"  [arg-type]
- pydantic/experimental/arguments_schema.py:43: error: Argument 1 to "_arguments_v3_schema" of "GenerateSchema" has incompatible type "Callable[..., Any]"; expected "FunctionType | MethodType | partial[Any]"  [arg-type]
+ pydantic/experimental/arguments_schema.py:43: error: Argument 1 to "_arguments_v3_schema" of "GenerateSchema" has incompatible type "Callable[..., Any]"; expected "FunctionType | MethodType[[VarArg(Any), KwArg(Any)], Any] | partial[Any]"  [arg-type]

dd-trace-py (https://github.com/DataDog/dd-trace-py)
- ddtrace/internal/wrapping/context.py:642: error: Argument 1 to "is_wrapped" of "_UniversalWrappingContext" has incompatible type "MethodType"; expected "FunctionType"  [arg-type]
+ ddtrace/internal/wrapping/context.py:642: error: Argument 1 to "is_wrapped" of "_UniversalWrappingContext" has incompatible type "MethodType[[VarArg(Any), KwArg(Any)], Any]"; expected "FunctionType"  [arg-type]
- ddtrace/internal/wrapping/context.py:645: error: Argument 1 to "get_function_code" has incompatible type "MethodType"; expected "FunctionType"  [arg-type]
+ ddtrace/internal/wrapping/context.py:645: error: Argument 1 to "get_function_code" has incompatible type "MethodType[[VarArg(Any), KwArg(Any)], Any]"; expected "FunctionType"  [arg-type]
- ddtrace/internal/wrapping/context.py:710: error: Argument 1 to "get_or_create" of "_ContextRecord" has incompatible type "MethodType"; expected "FunctionType"  [arg-type]
+ ddtrace/internal/wrapping/context.py:710: error: Argument 1 to "get_or_create" of "_ContextRecord" has incompatible type "MethodType[[VarArg(Any), KwArg(Any)], Any]"; expected "FunctionType"  [arg-type]
- ddtrace/internal/wrapping/context.py:711: error: Argument 2 to "link_function_to_code" has incompatible type "MethodType"; expected "FunctionType"  [arg-type]
+ ddtrace/internal/wrapping/context.py:711: error: Argument 2 to "link_function_to_code" has incompatible type "MethodType[[VarArg(Any), KwArg(Any)], Any]"; expected "FunctionType"  [arg-type]
- ddtrace/internal/wrapping/context.py:712: error: Argument 1 to "set_function_code" has incompatible type "MethodType"; expected "FunctionType"  [arg-type]
+ ddtrace/internal/wrapping/context.py:712: error: Argument 1 to "set_function_code" has incompatible type "MethodType[[VarArg(Any), KwArg(Any)], Any]"; expected "FunctionType"  [arg-type]
- ddtrace/internal/wrapping/context.py:718: error: Argument 1 to "is_wrapped" of "_UniversalWrappingContext" has incompatible type "MethodType"; expected "FunctionType"  [arg-type]
+ ddtrace/internal/wrapping/context.py:718: error: Argument 1 to "is_wrapped" of "_UniversalWrappingContext" has incompatible type "MethodType[[VarArg(Any), KwArg(Any)], Any]"; expected "FunctionType"  [arg-type]
- ddtrace/internal/wrapping/context.py:721: error: Invalid index type "MethodType" for "WeakKeyDictionary[FunctionType, _ContextRecord]"; expected type "FunctionType"  [index]
+ ddtrace/internal/wrapping/context.py:721: error: Invalid index type "MethodType[[VarArg(Any), KwArg(Any)], Any]" for "WeakKeyDictionary[FunctionType, _ContextRecord]"; expected type "FunctionType"  [index]
- ddtrace/internal/wrapping/context.py:723: error: Argument 1 to "get_function_code" has incompatible type "MethodType"; expected "FunctionType"  [arg-type]
+ ddtrace/internal/wrapping/context.py:723: error: Argument 1 to "get_function_code" has incompatible type "MethodType[[VarArg(Any), KwArg(Any)], Any]"; expected "FunctionType"  [arg-type]
- ddtrace/internal/wrapping/context.py:782: error: Argument 1 to "set_function_code" has incompatible type "MethodType"; expected "FunctionType"  [arg-type]
+ ddtrace/internal/wrapping/context.py:782: error: Argument 1 to "set_function_code" has incompatible type "MethodType[[VarArg(Any), KwArg(Any)], Any]"; expected "FunctionType"  [arg-type]
- ddtrace/internal/wrapping/context.py:785: error: No overload variant of "get" of "WeakKeyDictionary" matches argument type "MethodType"  [call-overload]
+ ddtrace/internal/wrapping/context.py:785: error: No overload variant of "get" of "WeakKeyDictionary" matches argument type "MethodType[[VarArg(Any), KwArg(Any)], Any]"  [call-overload]
- ddtrace/internal/wrapping/context.py:789: error: No overload variant of "pop" of "WeakKeyDictionary" matches argument types "MethodType", "None"  [call-overload]
+ ddtrace/internal/wrapping/context.py:789: error: No overload variant of "pop" of "WeakKeyDictionary" matches argument types "MethodType[[VarArg(Any), KwArg(Any)], Any]", "None"  [call-overload]