Update target platform to r2024-09

[tortmayr]

What it does

• Update target platforms.
  -New default target Eclipse 2024-09
  • New minimum baseline Eclipse 2023-12
  • Switch to jarkarta variant of lsp4j websocket
  • Switch to Jetty 12

Builds on top of: #24

Changes done on top:

• Remove outdated targets
• Adjust version ranges
• Create a new target definition for the minimum supported version (2023-12)
• Restore explicit reexport of certain packages to maintain backwards compatibility
• Fix and align m2 build
• Add possibility to change the target platform of the p2 build with the p2.target property

Part of eclipse-glsp/glsp#1397

How to test

Building and running the example via CLI should work as expected
Test the following:
P2:

• mvn clean verify -Pp2
• mvn clean verifiy -Dp2.target=r2023-12 (to build against the minimum p2 target)
  M2:
• mvn clean verify -Pm2
  Build the example fatjar
• mvn clean verify -Pm2 -Pfatjar
  Start the example jar
• java -jar examples/org.eclipse.glsp.example.workflow/target/org.eclipse.glsp.example.workflow-2.3.0-SNAPSHOT-glsp.jar -p 80
  81 --websocket
  (and open the example diagram.html of the standalone client example)

Eclipse version used for development: 2024-06 Modelling Tools
Also tested with 2023-12 Modellingtools

Follow-ups

Changelog

• This PR should be mentioned in the changelog
• This PR introduces a breaking change (if yes, provide more details below for the changelog and the migration guide)

[martin-fleck-at]

Change looks good to me, thank you very much, Tobias! I built and ran the server from maven and directly from Eclipse. It all seemed to work as expected. I just have a minor comment but nothing too important.

[tortmayr]

@martin-fleck-at The target for r2023-12 has been updated to use elk 0.8.1