This converts the numpy.ma.core._frommethod method wrapper utility class to a function, and modifies the wrapped inspect.signature to match that of the wrapper.

Before:

In [2]: np.ma.compress
Out[2]: <numpy.ma.core._frommethod at 0x7559fd926ea0>

In [3]: inspect.signature(np.ma.compress)
Out[3]: <Signature (a, *args, **params)>

After:

In [2]: np.ma.compress
Out[2]: <function numpy.ma.core.compress(condition, a, axis=None, out=None)>

In [3]: inspect.signature(np.ma.compress)
Out[3]: <Signature (condition, a, axis=None, out=None)>

As you can see in the "before" output, the a parameter was incorrectly reported as being the first one, which isn't the case. That's why I've labeled this as a bug.

Before this, it wasn't possible to meaningfully annotate these _frommethod functions, as stubtest did not recognize them as functions, but rather as instances of the _frommethod type. But now that they're actual functions (i.e. instances of FunctionType), we can annotate them like any other function, allowing us to use overloads and such.

Note that there's also a similar situation for np.ma.core._convert2ma. But I figured I'd first start with this one in case there are any objections, and otherwise address _convert2ma in a follow-up.

Note that stubtest will not like this, so I'll now be working on updating the stubs. I'm not planning on touching core.py anymore, so that part can already be reviewed. (I'll have to do a quick scipy-stubs release in the meantime though.)