Support for complex properties

There are some property which are complex composed by java classes (which implement some interfaces), package names, etc

Here some usecase:

log category

See https://quarkus.io/guides/logging#category-example

quarkus.log.category."io.quarkus.smallrye.jwt".level=TRACE
quarkus.log.category."io.undertow.request.security".level=TRACE

In this sample,we should have completion for package names (after category) and validation.

mp rest priority

com.mycompany.remoteServices.MyServiceClient/mprest/providers/com.mycompany.MyProvider/priority = 1

In this sample we should have completion for mp rest provider (after /providers). mp rest provider is a class which implements some interfaces. We should have too definition on this provider class, hover and validation.

The issue names no files, tests, or entry points. Start by investigating how configuration properties are modeled and completed for the logging-category and MP REST examples, then define support for package and provider-class completion, definition, hover, and validation. Done means both examples provide the requested language-server features.