Fix qbs install

[Psy-Kai]

Currently the qbs build helper installed its files into conanfile.install_folder. With this PR the files are installed directly in the conanfile.package_folder like cmake does.

Changelog: Fix: Build helper qbs install now installs directly into package_folder.
Docs: omit

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[memsharded]

Thanks for continuing on this.
The truth is that the target folders is not always clear, we are working trying to improve this, making it a bit more explicit, please keep tuned.

Merging this for next 1.35