Bump eclipse 2020-12

[dvojtise]

Description

This bump the base Eclipse to Eclipse 2020-12

This allows to solve start issue on MacOS

Changes

It also bump other components:

• Xtend/Xtext to 2.24.0
• Tycho to 2.2.0

Contribution to issues

Contribute to #
Closes #

Companion Pull Requests

• PR https://github.com/eclipse/gemoc-studio/pull/219
• PR https://github.com/eclipse/gemoc-studio-modeldebugging/pull/183
• PR https://github.com/eclipse/gemoc-studio-execution-java/pull/14
• PR https://github.com/eclipse/gemoc-studio-moccml/pull/17
• PR https://github.com/eclipse/gemoc-studio-execution-moccml/pull/49