cmSystemTools: Add EnvDiff class to hold ENVIRONMENT_MODIFICATION logic
Move the logic implementing the ENVIRONMENT_MODIFICATION
test property from cmCTestRunTest
to cmSystemTools
and encapsulate it in a new EnvDiff
class.
During development, I manually noticed that I had broken reset:
, so I added a regression test to protect against future breakages.
This MR splits out the refactoring steps from !7571 (merged) as requested by @brad.king
Topic-rename: refactor-environment-modification
Edited by Brad King