[effects] Rewrite the Dim Inactive effect

Summary:
The Dim Inactive effect was rewritten mostly to fix most of issues with
it, e.g. after leaving a full screen effect(e.g. Desktop Grid) windows
sometimes are not dimmed back, or when a window becomes inactive there
is no smooth transition, etc.

{F5956124}
//Before: the window is not smoothly dimmed.//

{F5956127}
//After: the window is smoothly dimmed.//

In combination with an effect that animates the disappearing of windows,
e.g. Glide, the rewritten Dim Inactive effect doesn't "flash" windows.
If an active window has been closed, it will stay bright. If an inactive
window has been closed, it will stay dimmed.

Among other changes, the KCM has been re-designed to follow common KCM
design in Plasma:

{F5956128, layout=center, size=full}

The way the rewritten Dim Inactive effect handles flashing/flickering problem can be
reused in the Dialog Parent effect.

### Demo

{F5959885}
//Before: dimming of a window group.//

{F5959886}
//After: Dimming of a window group.//

Depends on D13740

CCBUG: 359251

Test Plan:
Test plan #1
* Activated the Desktop Grid effect
* Dimmed windows smoothly brightened
* Left desktop grid
* Windows dimmed back

Test plan #2
* Opened Dolphin and its Preferences window
* Clicked on desktop, both Dolphin and the Preferences window dimmed
* Clicked on Dolphin, both windows smoothly brightened back

Reviewers: #kwin, #plasma, #vdg, davidedmundson

Reviewed By: #kwin, #plasma, #vdg, davidedmundson

Subscribers: davidedmundson, abetts, ngraham, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D13720