[structure view] show catalog definition location when hovering over a stereotype node

[martinlippert]

When hovering over a stereotype node in the structure tree, a hover should show up, displaying the location where the stereotype was defined (the URL of the catalog JSON file where this stereotype is defined)

[martinlippert]

Changed this from clicking on the node label to a separate inline action that appears on stereotype nodes, which then can be used to navigate to the referenced catalog file.

[martinlippert]

Navigating to catalog files from inside JAR files doesn't yet work properly, so re-opening this again.

[BoykoAlex]

@martinlippert do we have a project with stereotype JSON files in JAR dependencies to try? I think it'd work now for the default JSON files kept inside spring boot ls, will work for json files inside the workspace somewhere but may not work for JSON on the projects's classpath JARs... at least I'm not completely convinced they'd work...