Fading PS container on hide.

This change adds a fading effect to the PS
container when Space is locked with
"hide when locked" toggle enabled.

Video: https://photos.app.goo.gl/pqhsvhfBqkTcbHXa9
GPU Profile Video: https://photos.app.goo.gl/V9yLYDH4EtAZZNrt8
before: https://drive.google.com/file/d/1bThcu34w2kgiJhgeGSmeZY_lVnMgCdsQ/view?usp=sharing
after: https://drive.google.com/file/d/1ceI3A8UXyx7GYDfHGRkN8Wkzoi-01OVh/view?usp=sharing

Bug: 299294792
Test: Manual Flash
Flag: None Animation tweak.
Change-Id: I742036f43605ca9a64f0d0a22c86b3fd69223456