Merge topic 'refactor-environment-modification'

a5d45e685f Tests: Add case for ENVIRONMENT_MODIFICATION property OP=reset behavior
e2854b4fa2 cmCTestRunTest: Implement the ENVIRONMENT test property with EnvDiff too
bfa1c5285b cmSystemTools: Add EnvDiff class to hold ENVIRONMENT_MODIFICATION logic
a0b1c4ee90 cmCTestRunTest: Simplify by using GetSystemPathlistSeparator
4e6cbb1f13 cmCTestRunTest: Remove unnecessary CMAKE_BOOTSTRAP guard

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !7572