Add advanced "Generate getters and setters..." source action

[fbricon]

If a class has more than one field, and the client supports it, we should provide a way to select which fields will be used for getters/setters generation (similar to equals/hashcode selection).
The source action label should have the ellipsis (...) showing a dialog will be opened after selecting the action.
Clients that don't support the prompt workflow would receive the legacy source action.
Sources with a single field don't need the selection workflow, obviously, so again, the legacy source action should be returned.