Prevent abseil-cleanup-ctad check from stomping on surrounding context

This change applies two fixes to the abseil-cleanup-ctad check. It uses hasSingleDecl() to ensure only declStmt()s with one varDecl() are matched (leaving compount declStmt()s unchanged). It also addresses a bug in the handling of comments that surround the absl::MakeCleanup() calls by switching to the callArgs() combinator from Clang Transformer.

Reviewed By: ymandel

Differential Revision: https://reviews.llvm.org/D115452