[clang] [llvm] [clang][CoverageMapping] Refactor when setting MC/DC True/False (PR #78202)

[Alan Phipps via cfe-commits]

evodius96 wrote:

> I've found this change fails with the expression; `((a && (b || c) || (d && e)) && f)`.

Thank you for pointing this out.  I think you figured out the point I was struggling to get right -- when to actually "pop" the child Decision from the stack, and also to separate the "pop" operation from the calculation of the total conditions.  I was constrained by the design.  I like your cleanup, including the removal of the NestLevel stack, so I integrated most of your refactor.

https://github.com/llvm/llvm-project/pull/78202