Audit uses of FilePath::withExecutableSuffix()

We have around 100 uses of FilePath::withExecutableSuffix() that might not be needed, and in the context of cross Window->*nix setups even be harmful, see https://bugreports.qt.io/browse/QTCREATORBUG-31939.

As first approximation: FilePaths that are actually used to start processes will likely not need it, but FilePaths used elsewhere (e.g. comparisons with others) may need it.

Would be good to remove the ones that are not needed and to add a short comment why they are needed on the ones that are needed.