Customizable merger per view type

[kmrozek-siili]

Currently merging strategy is coupled with VDOM merger and cannot be customized. You cannot create specific strategy for your own view type. This is important for couple of reasons:

1. It could fix in elegant way, problem with text input position. We could create specific view type for input that supports storing text position before updating text and restore it after that. It
2. It would allow to create custom views to implement integrations with foreign libraries (like Codemirror or Leaflet).

Possible solution is add specific "class" - ViewMerger that would implement methods like

• merge - move functions like mergeTag, mergeText from VDOM createMerger
• createNode - remove node() method from View and decouple it from View
• finishAttach - called after node creation
• prepareDestroying - called before node destroy

Additional class ElementViewMerger would contain specific methods like

• setProperty - here we would fix input field issue

ViewMergers would be declared in createMerger call. Couple of ViewMergers would be declared by default. It would be ElementViewMerger, TextViewMerger and InputViewMerger.