Unify and simplify the behavior of the hasDeclaration matcher.

Originally, we weren't able to match on Type nodes themselves (only QualType),
so the hasDeclaration matcher was initially written to give what we thought are
reasonable results for QualType matches.

When we chagned the matchers to allow matching on Type nodes, it turned out
that the hasDeclaration matcher was by chance written templated enough to now
allow hasDeclaration to also match on (some) Type nodes.

This patch change the hasDeclaration matcher to:
a) work the same on Type and QualType nodes,
b) be completely explicit about what nodes we can match instead of just allowing
   anything with a getDecl() to match,
c) explicitly control desugaring only one level in very specific instances.
d) adds hasSpecializedTemplate and tagType matchers to allow migrating
  existing use cases that now need more explicit matchers

Note: This patch breaks clang-tools-extra. The corresponding patch there
is approved and will land in a subsequent patch.

Differential Revision: https://reviews.llvm.org/D27104

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@309809 91177308-0d34-0410-b5e6-96231b3b80d8