[Java/Spring] all-of and one-of Improvements and Fixes (was #12075)

Created by: cachescrubber

Fix Bug in OneOfImplementorAdditionalData pulling in wrong vars to one-of-implementors. Support parentVars in order to support fluent setter with inherited properties.

This PR fixes a Bug in OneOfImplementorAdditionalData which pulls in parent properties in a one-of implementor when the one-of implementor also inherits form a parent using all-of.

In order to use the fluent setter methods for models using inheritance, all Models are post processed and the CodegenModel.parentVars are set up to recursive include all parent properties incl. all necessary imports. Squashed commit of the following:

This PR replaces #12075 after merge problems.

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