Store implicit specializations as distinct symbols in the index, with their own refs

[HighCommander4]

Currently, a usage of an implicit template specialization is stored as a ref to the template decl in the index.

It would be useful to be able to find references to a specific specialization only, even if it's an implicit specialization. This would require creating distinct symbols for implicit specializations, with their own refs.

This suggestion originally came up here.

[kadircet]

It is important to note that this likely implies a huge size increse in index. So would be nice to see some numbers with a quick prototype, if someone decides to implement this in the future.