devel/qtcreator: update to 6.0.2, cmake build

Update to most-recent release and switch the build to CMake
(which matches the general migration of Qt to using CMake for
builds). While here, drop the qbs dependency because qbs is
broken with newer clang.

Thanks to Florian for a carefully-written update and PR.

Obtained From: Florian Walpen
PR: 262078