Invert setFactoryResetProtectionDisabled

* Invert and rename setFactoryResetProtectionDisabled
  to setFactoryResetProtectionEnabled.
* Invert and rename isFactoryResetProtectionDisabled
  to isFactoryResetProtectionEnabled.
* Update javadoc for both APIs.

Bug: 148596230
Test: atest com.android.server.devicepolicy.DevicePolicyManagerTest
      atest com.android.server.devicepolicy.FactoryResetProtectionPolicyTest
      atest com.android.cts.devicepolicy.MixedDeviceOwnerTest#testFactoryResetProtectionPolicy
      atest com.android.cts.devicepolicy.OrgOwnedProfileOwnerTest#testFactoryResetProtectionPolicy

Change-Id: I0e0b7d0bec8d10ffa4ef4a2d9fa4b60d7b3a94c1