Simplify communication between JDT LS & Quarkus LS

[angelozerr]

This issue is to study how simplifying communication between JDL LS and Quarkus LS in term of code:

• writing no code on client side (typescript) (or just line of code to register the Quarkus langage client in the Java language client)
• on JDL LS extension using LSP4J annotation for notification, request (like LSP TextDocumentService) instead of using a delegate command handler (we will able to to use POJO instead of Map arguments)

This issue concern:

• JDT LS
• vscode-java
• vscode-quarkus

[angelozerr]

We have implemented a POC with this idea, see https://docs.google.com/document/d/1HHC39OVcenfF7bxhhaQO8rgMgyX_YVBzx-arUKpDnCE/edit#heading=h.gjdgxs