[clang-tidy] Remove unnecessary getName() on Decls and Types feeding into a Diagnosti...

[clang-tidy] Remove unnecessary getName() on Decls and Types feeding into a DiagnosticBuilder

Going through a string removes some of the smarts of the diagnosic printer
and makes the code more complicated. This change has some cosmetic impact
on the output but that's mostly minor.

llvm-svn: 265680