Add new dpm api to disable user control over apps

Setting a package as protected prevents user from clearing app data and
force stopping apps from Settings and Launcher. Added two apis
* setProtectedPackages()
* getProtectedPackages()

Bug: 135486391
Test: atest DevicePolicyManagerTest
Change-Id: I28858aca89a52ba06af033a24da43f394ed79a0e