Description
When using a USS filter, the output of the filter is premultiplied but is then used as a regular (non-pre-multiplied) texture.

Initial setup
Create an empty URP project but use gamma color space for simplicity

Reproduction steps

• Remove the cameras
• Add a UIDocument in the scene
• Create a UXML template and assign it to the UIDocument
• Create a PanelSettings that clears the background to black and assign it as well.
• Open the template in the UI Builder
• Create a white rectangle with 50% alpha
• Set the opacity filter to 1 (fully opaque)

Expected behaviour
The observable color should be a mid-gray rectangle

Actual behavior
The observable color is much darker