[FEATURE] Background Blur Support

[Mikolaytis]

Is your feature request related to a problem? Please describe.

We need a fast way to draw a good background blur. Now we are doing it ourselves - getting bad performance results.
Here is a page with examples of what we want: https://webkit.org/blog/3632/introducing-backdrop-filters/

Describe the solution you'd like

I've found a solution here: https://bugs.chromium.org/p/skia/issues/detail?id=4915
Skia has this method https://api.skia.org/structSkCanvas_1_1SaveLayerRec.html
Can SkiaSharp implement it?

Describe alternatives you've considered
I think there is also a way to implement a shader that will do the same effect. But I didn't found any example how to do things like this. Also I have a super basic shader experience.

[tamasszadvari]

+1 for this feature. Background blur is widely used by designers, so it would be important to make it available.

[michaldobrodenka]

Probably dependent on this #2962