Publish langium packages as scoped packages

[msujew]

Currently all of our packages (except for the core framework) use the langium-<name> structure like langium-cli or langium-railroad. We should maybe think about putting them under the @langium scope and rename the core framework package to @langium/core, with others being @langium/cli and @langium/sprotty.

Please discuss this change here.

[spoenemann]

What are the benefits compared to the current situation?

The only thing that comes to my mind is the ability to block a namespace so only the Langium project team can publish a package @langium/*.