Move code from SuggestionChecks to FeatureProvider

This is step one to deprecate SuggestionChecks. Moving logic into
SuggestionFeatureProvider allows potential logic override and improves
testability.

Also moved isSuggestionComplete tests to corresponding activity/pref
controller test.

Bug: 65065268
Test: robotests
Change-Id: I2071d30fc58bb84acad2083ca03cfcf7d41f10cb