[analyzer][NFC] Refactor functions in PlistDiagnostics to take AnalyzerOptions as parameter

I intend to add a new flag macro-expnasions-as-events, and unfortunately
I'll only be able to convert the macro piece into an event one once I'm
about to emit it, due to the lack of an avaible Preprocessor object in
the BugReporter.

Differential Revision: https://reviews.llvm.org/D52787

llvm-svn: 343620