[clang] [clang][analyzer] Add plist macro formatting (PR #156046)

[Balazs Benics via cfe-commits]

steakhal wrote:

> Can't find any unit tests for methods in PlistDiagnostics.cpp
> 
> So adding the unit test in `clang/unittests/Analysis/MacroExpansionContextTest.cpp` Since it contains some similar MacroExpansionContextTest functionality tests. Also, since the newly defined function `getFormattedMacro` is static , should i just duplicate it in the testing file or how should i proceed ?

Yes, I had `MacroExpansionContextTest` in mind, exactly.

Wrt. the second part; would it make sense to move this formatting functionality into the `MacroExpansionContext`?
I'd go as far as caching these formatted strings for the expansion locations to avoid potential duplicated queries. Frequently, bug reports cross the same macro expansions by nature, thus this might save some time. WDYT?

https://github.com/llvm/llvm-project/pull/156046