[+TASK] Cleanup and small improvements to Interceptors
Interceptors now also get passed the current Parsing State,
which they can use to interact with the tree. This can be helpful
to add new syntax tree elements dynamically after or before the
current one. While this functionality is not yet used inside Fluid,
it is used inside a package I am currently developing.
Furthermore, made TextboxViewHelper extend TextFieldViewHelper,
as TextboxViewHelper is deprecated, and TextFieldViewHelper is