Added new APIs to let Settings enable / disable ContentCapture

Bug: 123286662
Test: atest ChildlessActivityTest#testSetContentCaptureFeatureEnabled_disabledBySettings \
        ChildlessActivityTest#testSetContentCaptureFeatureEnabled_disabledThenReEnabledBySettings\
        FrameworksCoreTests:SettingsBackupTest#secureSettingsBackedUpOrBlacklisted
Test: atest CtsContentCaptureServiceTestCases # for sanity check

Change-Id: I7cd2c36c1d7e23efb9acacf4f18cecd8838f5ac5