Add global checknotnull.flags Proguard config

# Tell R8 that the following methods are check not null methods, and to

# replace invocations to them with a more concise nullness check that produces

# (slightly) less informative error messages

-convertchecknotnull class com.google.common.base.Preconditions {

  ** checkNotNull(...);

}

-convertchecknotnull class java.util.Objects {

  ** requireNonNull(...);

}

-convertchecknotnull class kotlin.jvm.internal.Intrinsics {

  void checkNotNull(...);

  void checkExpressionValueIsNotNull(...);

  void checkNotNullExpressionValue(...);

  void checkReturnedValueIsNotNull(...);

  void checkFieldIsNotNull(...);

  void checkParameterIsNotNull(...);

  void checkNotNullParameter(...);

}

-convertchecknotnull class dagger.internal.Preconditions {

  ** checkNotNull*(...);

}