When I introduced hard-coded formatters, I made them non-cacheable

This is because - in theory - the formatter could match on not just the type, but also other properties of a ValueObject, so a per-type caching would not be a good thing
On the other hand, that is not always true - sometimes the matching truly is per-type

So, introduce a non-cacheable attribute on formatters that decides whether a formatter should or should not be cached. That way, the few formatters that don't want themselves cached can do so, but most formatters (including most hard-coded ones) can cache themselves just fine

llvm-svn: 241184