Track SUT app lifetime in system tests (PR #14289)
- Tracking of the System Under Test (SUT) application (I.E. Notepad, Chrome) was not accurate, instead, the "start.exe" app was being tracked.
* Use the `wait` argument for start. This isn't failsafe, some applications (E.G. Chrome) will exit immediately if there is already a "controller" process running.
* Use the expected window title to find the applications window handle to track it.
- Instance variables in robot libraries are reset for teardown, the SUT app cannot be tracked if the window handle is lost.
* Use class variables on Robot library classes so that the variables survive through different phases of the test.
- Many chrome tabs in appveyor may cause slowdowns, and chrome crashes.
* Close chrome tab after tests complete, chrome sometimes crashes on appveyor, possibly due to memory limitations.
- Attempting to close notepad (with alt+F4) can result in closing developer tools when notepad is not the foreground application.
* Only close notepad if it is the foreground window, prevent closing developers' tools when focus shifts.
