Fix deadlock in showing Toast for sensitive content

Toast#show calls into NotificationManagerService which then acquires a
lock there.

WMS is at a lower layer of the system and shouldn't be calling into a
higher level system with a lock held. This cl fixes the layering
inversion.

Bug: 323580163
Test: atest CtsSensitiveContentProtectionTestCases:android.sensitivecontentprotection.cts.ViewSensitiveContentTest --iterations
Change-Id: I4e829183b7f29ad2ad3231f4ea91937b8d9e2c6b