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

[via cfe-commits]

ankurkraj 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 ?

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