Fast Crop filter not working properly on objects with alfa channel.

Summary:

The new Fast Crop filter uses a Composite effect with the Over operator. It is supposed to do nothing but it changes the colors of objects with transparent pixels.
A different operator should be used.

Steps to reproduce:

open Inkscape
draw an object with RGBA color #00000080
apply Fast Crop filter to that object

What happened?

The original object (#00000080):

After applying the filter:

Object apears as if the color was set to #000000BF.
This of course also applies to imported bitmaps making this filter unusable for cropping bitmaps with transparency.

- Inkscape Version: Inkscape 1.2-dev (b270682, 2021-05-01)
- Operating System: Win10 64-bit

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