Use GEF version 3.20 #62
Description
This allows to benefit of eclipse-gef/gef-classic#426 and the new corresponding APIs. These new APIs, will be used afterward in Sirius to clean code done for eclipse-sirius/sirius-desktop#359. Currently, the code corresponding to these new APIs has been duplicated no Sirius side (for example in PR 360).
Version GEF 3.20 will be probably released for Eclipse 2024.06.