[ASTImporter][NFC] Dump decl name at assertion violation

Sometimes it would be useful to see which Decl kind caused some issue,
along with the name of the concrete instance of the Decl in the source
code.

Reviewed By: martong

Differential Revision: https://reviews.llvm.org/D113668

GitOrigin-RevId: f3753ad774506804ef5df065b48268712bdaa554
1 file changed