Move to JavaSE-17

[pcdavid]

The oldest supported target platform (2020-09) requires Java 11 so there is not much point to declare a BREE of JavaSE-8.

[pcdavid]

Updated to switch to Java 17 directly.

[pcdavid]

This would be the opportunity to regenerate the code using more "modern" settings.

• Target Java 17.
• Use (relevant) EMF features which did not exist in.. EMF 2.2 (the Runtime Version mentioned in the genmodel).

Note that the GMF Notation metamodel is essential API for a lot of downstream projects (GMF Runtime of course, but everything that uses it, including Sirius for example). Any API break should be well thought of and advertised with enough time for projects to adapt.

Also, at least CDO contains its own version of this metamodel, generated with different settings (in this case, to create native CDO EObjects). We should coordinate the change with them.