Improve VSCode config

[tobiasdiez]

• Add gradle extension
• Add basic vscode config for checkstyle and formatting

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[tobiasdiez]

@Siedlerchr can you please export the eclipse code formatter config as xml and add it here? Thanks!

Eclipse's Preferences → Java → Code Style → Formatter and export the settings to an XML file via the Export All button (or Edit and then Export in dialog that opens up)

[Siedlerchr]

The key problem is that the eclipse code formatter is still not compatible with intelij regarding indentation. This will create chaos if people start using it

[tobiasdiez]

So how do you format your code then in eclipse?

[Siedlerchr]

I try to not format my code in Eclipse, at least I only execute it for a method or so and manually fix the indentation afterwards. The problem is that for wrapped lines I haven't found a way.
I uploaded the current generated style

jabref2.xml.txt

[tobiasdiez]

Thanks, it's not perfect as you say, but better than nothing.