CGAL Lab: Add a target CGALlab_compile_all_plugins

[lrineau]

Summary of Changes

Fix a usability issue with Visual Studio Code. There is now a new target CGALlab_compile_all_plugins that compiles the executable CGALlab and all the plugins.

That target, as seen in the vscode Make Project Outline, is placed just below the CGALlab target.

If the executable CGALlab_compile_all_plugins is launched, it just displays:

This executable is not intended to be run.
Please run the CGALlab executable instead.

Release Management

• Affected package(s): Lab

[sloriot]

Successfully tested in 6.0-Ic-251