Add prioritized enableCarMode API in UiModeManager

Per design doc (go/android-car-mode-design), added new system API to
enable car mode and specify a priority for the calling app.
Also modified UiModeManager to pass the package name of the caller to
UiModeManagerService.

Bug: 136109592
Test: Added new unit tests and CTS tests.
Test: Added Telecom test app functionality to verify.
Change-Id: I2848039c9ea18ba93e7694e04c4e5dc70759daa3