Add parent selector for window rules

[Enovale]

Firstly, the use case: I want to be able to put any game launched through steam on a certain workspace. This can be done for all Proton games via this rule:

windowrule = workspace 7, class:^(steam_app_.*)$

But not all games are launched this way. Certain compatibility tools can change this behaviour, and any actually native Linux game will not launch this way, it's title and class are up to the specific application in question.

An elegant way to fix this, would be a rule something like this:

windowrule = workspace 7, class:^(?!steam$),parent:^(steam)$

And assuming the parent selector is matching against the class of all parents of a window, it would solve my issue without any false positives.

I would assume a similar approach could be borrowed from the implementation of swallowing, but that may not be very performant.