[Settings] Code refactor for IMS part

Return boolean in method names starting with "is".

Bug: 140542283
Test: m RunSettingsRoboTests -j ROBOTEST_FILTER=Enhanced4gBasePreferenceControllerTest
Test: m RunSettingsRoboTests -j ROBOTEST_FILTER=Enhanced4gLteSliceHelperTest
Test: m RunSettingsRoboTests -j ROBOTEST_FILTER=VideoCallingPreferenceControllerTest
Change-Id: I2a9ca9ae829f0dcda478f3343cd50e61f441a9a7
8 files changed