Set FLAG_DIM_BEHIND for Bidics Prompt window

Biometric prompt used to set a background color
biometric_dialog_dim_color for dim effect, however
the dim background did not cover the statusbar and
navigationbar regions.

Use window manager approach for dim effect:
- Set FLAG_DIM_BEHIND for window layout params
- Set 0.5f dimAmount
- Transit dimAmount when animate away

Test: atest SystemUITests
Test: atest com.android.systemui.biometrics.AuthContainerViewTest
Test: enroll FPS, long press wifi hotsopt QS tile, then
      tap "Share" affordance with the QR code icon to
      bring up the biometric prompt
Bug: 237047065

Change-Id: Icbb68406357a000a61752bd03d9337acf0eb6276