If the PATH modification choice has not been saved persistently by an
existing installation of CMake, default to modifying the system PATH
environment variable to make our command-line tools available for all
users. This is a common expectation.
Fixes: #21465
Our Windows installer provides an interactive dialog to choose whether
the PATH should be modified. It may also be specified on the `msiexec`
command-line as an `ADD_CMAKE_TO_PATH={0,1}` property. Save the choice
persistently in the Windows Registry and use the same choice by default
in future installations.
Issue: #21465