It has been requested that PyInstaller.isolated be made reusable
by other, permissively licensed projects. (#7386)

That portion of the codebase has so far only picked up two contributors
and can therefore be re-licensed with just the consent of those two.

Signed-off-by: Brénainn Woodsend <bwoodsend@gmail.com>
Signed-off-by: Rok Mandeljc <rok.mandeljc@gmail.com>