[SofaCUDA] GUI: create extension to use Sofa.GUI with SofaCUDA

[fredroy]

based on

• [SofaCUDA] move Qt-related code #5968

Move the GUI-related part to an extension plugin SofaCUDA.GUI
and set the dependency on the narrower Sofa.GUI.Common

breaking 'cause one must now loadplugin SofaCUDA.GUI in their scene

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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).