Fix STATE_DEPTH stuck at 1 after setting wallpaper

- Made BaseDepthController.setDepth/mDepth private, all get/set should be done through STATE_DEPTH or WIDGET_DEPTH
- Generified ClampedDepthProperty into Utilities.ClampedProperty to apply on STATE_DEPTH

Bug: 240580498
Test: Go to walppaper&style, set new wallpaper, then go to widget picker, wallpaper depth should transition smoothly
Change-Id: I53cdedf970fd7ffba6a952c4edf4b34251b01f07