[analyzer] Create MacroExpansionContext member in AnalysisConsumer

Adds a `MacroExpansionContext` member to the `AnalysisConsumer` class.
Tracks macro expansions only if the `ShouldDisplayMacroExpansions` is set.
Passes a reference down the pipeline letting AnalysisConsumers query macro
expansions during bugreport construction.

Reviewed By: martong, Szelethus

Differential Revision: https://reviews.llvm.org/D93223