Allow cached_property to be used on other methods

[FunkyBob]

This adds an optional name property to cached_property, overriding where it stores its cached value.

class Foo(object):
    def get_bar(self):
        ...heavy work...

    bar = cached_property(get_bar, name='bar')

Without the name, it would save the result in __dict__['get_bar'], thus masking the method.

[loic84]

Sounds good.

Since cached_property is documented, it'll need docs update and release notes.

[Tim Graham]

Actually, #22663 suggests to remove the documentation for cached_property. Second opinions welcome on that...

[Tim Graham]

I added docs in a comment on the PR; will go ahead and commit this if they look okay.

[Tim Graham <timograham@…>]

In 71461b14ab0c5a3801d85738fde3aedd407d7115:

Fixed #22691 -- Added aliasing to cached_property.