[clang][AST] Fix end location of DeclarationNameInfo on instantiated methods (#92654)

Fixes #71161

[D64087](https://reviews.llvm.org/D64087

) updated some locations of the
instantiated method but forgot `DNLoc`.

`FunctionDecl::getNameInfo()` constructs a `DeclarationNameInfo` using
`Decl::Loc` as the beginning of the declaration name, and
`FunctionDecl::DNLoc` to compute the end of the declaration name. The
former was updated, but the latter was not, so
`DeclarationName::getSourceRange()` would return a range where the end
of the declaration name could come before its beginning.

Patch by Alejandro Alvarez Ayllon
Co-authored-by: steakhal

CPP-5166

Co-authored-by: Alejandro Alvarez Ayllon <alejandro.alvarez@sonarsource.com>