[kcm/kwinrules] Detect also window complete class

Summary:
When detecting the properties of a window, now it shows and lets the user select the window complete class.
If this property is selected in the overlay, Window class takes the whole class value, and the option Match window whole class is set.

This adds back a feature the old kcm was offering.

BUG: 421542
FIXED-IN: 5.20

Test Plan:

• Detect window properties and pick a firefox window
• The property selector shows: Window class: navigator and Whole window class: navigator firefox
• Selecting the latter set the properties as per summary

Reviewers: ngraham, KWin, Plasma, meven

Reviewed By: ngraham, KWin, Plasma, meven

Subscribers: broulik, davidedmundson, meven, anthonyfieroni, zzag, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D29791