UI5 support flow through event handlers

[mbaluda]

See xss-event-handlers test

[jeongsoolee09]

Improvement sketch:

• doSomething1: Extend GetBoundValue and SetBoundValue to cover the division between doSomething1 and onInit.
  • The problem is that GetBoundValue and SetBoundValue is not identified for xss-event-handler, thus no isAdditionalFlowStep is identified.
• doSomething2: Implement a rudimentary parser for the expression bindings DSL, thus we can extract the handler name and the bound node inside the argument.
  • The problem is that the user input is replaced by parameter modelProperty. –> So there's no longer a link between /input and /output2.