Add code completion support for known type variables

[Gatar]

Please add code completion support (methods & fields) for two types of variables:

1. Functional variables used to drive ACM or available by default like inputs conditions formatter resourceResolver etc

2. Script variables of known type, explicitly declared, example:
   PageManager pageManager = resourceResolver.adaptTo(PageManager.class)
pageManager. <- code completion

[krystian-panek-vmltech]

this requires language server https://github.com/eclipse-jdtls/eclipse.jdt.ls but deploing such a thing on AEM may a bit cumbersome.
we could emulate it with reflection I think but I haven't found enough time to do PoC