Add access control to trySetWorkModeEnabled and make it public

Test: Quick Settings -> Toggle work mode
Test: Settings -> Work profile settings -> Toggle work mode
Test: Turn off work mode -> Settings -> Turn on work mode in the suggestion
Test: Turn on work mode through tapping on work app

Test: cts-tradefed run cts-dev --module DevicePolicyManager --test com.android.cts.devicepolicy.QuietModeHostsideTest

BUG: 70212757

Change-Id: I335c3ab2306a3eb794cd35a3a7b0d184dc31f85e