Add K as an alias for KeyTransform.from_lookup

[Paolo Melchiorre]

I propose to add K as an alias for KeyTransform.from_lookup

It's something possible to do in django.contrib.postgres before Django 3.1 and it can still be useful now to get non-textual data back from database.

This would be an example of use and I show the difference with KT

>>> qs = MyModel.objects.all()
>>> values = qs.values_list(
    K("value__true"),
    K("value__false"),
    K("value__none"),
    K("value__dict"),
    K("value__list"),
)
[True, False, None, {"k": "v"}, [None, True, False]]
>>> text_values = qs.values_list(
    KT("value__true"),
    KT("value__false"),
    KT("value__none"),
    KT("value__dict"),
    KT("value__list"),
)
["true", "false", "null", '{"k":"v"}', "[null,true,false]"]

[Mariusz Felisiak]

As far as I'm aware exposing a new API is unnecessary, F() should work just fine.