injected class name of a class template or class template partial specialization.
This is a non-canonical type; the canonical type is still a template
specialization type. This becomes the TypeForDecl of the pattern declaration,
which cleans up some amount of code (and complicates some other parts, but
whatever).
Fixes PR6326 and probably a few others, primarily by re-establishing a few
invariants about TypeLoc sizes.
llvm-svn: 98134