qmlls: trigger rebuilds on code completion requests

Currently, qmlls only triggers rebuilds when the file content of a .qml file changes.

Maybe it could also trigger rebuilds in case other actions are done on that .qml file, for example requestion code completion, asking for usages, etc. Maybe the LSP supports even notifications that the user "activate" one document?

Investigate if this is feasible, and whether that would make sense or not.