Commit ad7077c03daf ("Update FindPySide2Tools.cmake") removed the
versioned names of uic/rcc, which are at least used on openSUSE
and Fedora.
Instead of determining the path of uic/rcc manually, just use
the imported executable targets. rcc comes from QtCore, while
uic comes from QtWidgets.
Fixes#6445.
Found that on ubuntu 20.04 where QT is still at 5.12, these are called pyuic5 and pyrcc5 now and cmake will not find these and then the build fails without this change
Since PySide2 5.14, 'pyside2-rcc' and 'pyside2-uic' have been renamed into plain 'rcc' and 'uic'.
This leads FindPySide2Tools.cmake to no longer find rcc/uic, as reported in bug #4229 (https://www.freecadweb.org/tracker/view.php?id=4229) and prevents compilation.
FindPySide2Tools has been updated accordingly.
Non GNU sed on macOS expects suffix after -i option (can be empty str).
However, removing the comments from the pyside generated files is not a necessary
operation (presumably done to avoid a diff when no code changed), so simply skip the operation on macOS
