[IRGen] Fix LinkEntity::isTypeKind.
There are numerous entity kinds declared after
`ProtocolWitnessTableLazyAccessFunction` which aren't type kinds. Group
all those which are type kinds together for now. In the fullness of
time it would probably we wise to replace this implementation with a
switch statement so that when new kinds are added there is a chance that
the type-ness of that kind can be considered.