Allow selection of types from extended aspects for return and parameter types

[Matthias Schoettle]

Just as with mappings (for the to element the possible choices include elements from extended aspects), when changing a return type or parameter type, the possible choices should include valid types from extended aspects.

Setting component to Metamodel, because the possible choices are coming from the property descriptors.

[Matthias Schoettle]

Resolved issue #61: Filtering of choice of values also allows types from extended aspects.

In addition, a custom label provider prefixes types from other aspects with the aspect name to be able to distinguish where the type is coming from. In order to figure this out, the target is needed. Since item providers are state-less, the specific target is set in getChoiceOfValues. We know that getLabelProvider is called right after (respectively getChoiceOfValues gets called before).

Generally, though, there should be a) a filterChoiceOfValues that can also allow the extended aspects and not just the current one b) a label provider that does specializations, but can be used by different item providers (currently the same code is used in Operation and ParameterItemProvider).

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