[GUI] Remove Qt and make SofaImGUI as default viewer

[bakpaul]

This PR removes Qt from the sources of SOFA and makes SofaImGUI as the default GUI.

The Qt sources haven't bee pluginized yet, the repo is already here : https://github.com/sofa-framework/Sofa.Qt but I prefere to wait until this PR is merged to make the export, in case another PR modifying the sources is merged before.

[ci-depends-on https://github.com/sofa-framework/SofaGLFW/pull/141]

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By submitting this pull request, I acknowledge that
I have read, understand, and agree SOFA Developer Certificate of Origin (DCO).

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Reviewers will merge this pull-request only if

• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
• it does not generate new unit test failures.
• it does not generate new scene test failures.
• it does not break API compatibility.
• it is more than 1 week old (or has fast-merge label).

[bakpaul]

[ci-build][with-all-tests][force-full-build]