Add an editor warning when the variable's value is not modified in a setter or when nothing is returned from a getter

[mieldepoche]

Setter can sometimes contain complex logic and it's easy to forget to actually change the variable's value, especially when the setter's code contains "reaction" logic (as opposed to "validation" logic).

var x:
    set(value):
        # complex logic, forget to actually set x.

What about having an editor warning show up when the setter does not contains any x = ... statement?
Such warning could of course be dismissed with a proper anotation (not sure which exaclty).

Similarly, a getter can return nothing (null):

var x:
    get:
        pass

What about treating it the same as a regular methods, by showing an error when there's a path in which no explicit return is met?