Upgrade to Java 21

[MarkusAmshove]

• [x] Check for Gradle warnings
• [x] Check bytebuddy issue
• [x] Determine if publish would also publish fat jars
• [x] Update VSCode Deployment to download JDK 21 (MarkusAmshove/vscode-natural#42)

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud