Redact GridTaskViewThumbnail

This inherits from TaskViewThumbnail but has its own drawing logic that
skips work redaction for locked users. This is required by CTS Verifier,
so it needs to be done here as well.

Test: visual, instructions --
Test: (1) set up work profile on ryu with a password
Test: (2) turn screen off and on again
Test: (3) go to recents, verify work apps redacted with correct color
Test: (4) open a work app, unlock, go back to recents, verify work apps
Test:     are not redacted any more.
Bug: 34836435
Change-Id: I2239fe4c035332a9c9b93d2d2b1c354f204358a8