UI Toolkit 'background-size' property is not fully animatable

Reproduction steps:
1. Open the attached “AnimatableBackground.zip” project
2. Open the “test” Scene
3. Enter the Play mode
4. Hover on the image
5. Observe the animation

Expected result: The background-size property animation is fully animated
Actual result: The background-size property animation has discrete animation

Reproducible with: 2022.3.52f1, 6000.0.25f1, 6000.1.0a2
Couldn’t test with: 2021.3.45f1 (The background-size property did not work)

Reproducible on: Windows 11
Not reproducible on: no other environment tested