[ds annotations] provide hover text for component property types

[laeubi]

Component Property Types are very powerful, but the mapping rules are not really something to be processed by humans.

It would be therefore extremely helpful if

1. An annotation is annotated with the @ComponentPropertyType
2. I hover over one of the methods in that type
3. The javadoc popup shows the property that will be generated for this

Alternatively (or additionally) we can use an info marker so it is clear to what string representation such a method maps.