Optimize skip methods of JsonStructureParser

[marschall]

Optimize the following methods in JsonStructureParser

• skipObject
• skipArray

[marschall]

While the PR may look suspicious I believe the code is correct. The key insight is we are already working on a parsed JsonStructure, we just need to abort iterating on the current subtree. To stop iterating over the current subtree we do not need to advance the iterator to the end, we just need to pop the scope stack. To do this it is enough to set the current state to END_. #next() will then call #transition() which will pop the scope stack because the current state is END_.