Added noise blur effect

Summary:
Added the option to turn on noise behind the blurred area.
The lowest strength value disables it completely, so it is optional and is disabled by default.

Test Plan:
Edit: this new screenshot shows the updated noise generation.
Edit2: separated the screenshots so you can flick through them to clearly see the differences

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Reviewers: #kwin, #vdg, fredrik

Reviewed By: #vdg, fredrik

Subscribers: davidedmundson, matheusm, romangg, ivan, zzag, ngraham, kwin, #kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D10281