Show a warning toast when PiP is blocked in the streamed display

Add an API in DWPC to monitor the Pip is allowed in the streamed display
by policy controller. If not allowed, pop up a warning toast for user.

Bug: 229837382
Test: manually, atest WmTests:ActivityRecordTests
Change-Id: Id1f39e8b54cd9c388c49b3886b9e798144ba5bf1