chore(ui5-combobox): complexValue POC

[MapTo0]

Thats a POC for introducing a new property called complexValue. The idea is to have a single property representing the field value and the selected items. value property of the items serves as a key.

Since complexValue is type Array we need to change how Array objects are handled by the framework
@ilhan007 @vladitasev @pskelin @nnaydenow

Side effects: Array type properties are rendered in the DOM when noAttribute is set to false (or not set at all)

API

<!-- Input's value is "item 3" and the selected item's value is "3"  -->
<ui5-combobox complex-value='["item 3", "3"]'>
  <ui5-cb-item text="Item 1" value="1"></ui5-cb-item>
  <ui5-cb-item text="Item 2" value="2"></ui5-cb-item>
  <ui5-cb-item text="Item 3" value="3"></ui5-cb-item>
  <ui5-cb-item text="Item 4" value="4"></ui5-cb-item>
  <ui5-cb-item text="Item 5" value="5"></ui5-cb-item>
</ui5-combobox>

<!-- Input's value is "Some Value"  and no item is selected -->
<ui5-combobox complex-value='["Some Value", ""]'>
  <ui5-cb-item text="Item 1" value="1"></ui5-cb-item>
  <ui5-cb-item text="Item 2" value="2"></ui5-cb-item>
  <ui5-cb-item text="Item 3" value="3"></ui5-cb-item>
  <ui5-cb-item text="Item 4" value="4"></ui5-cb-item>
  <ui5-cb-item text="Item 5" value="5"></ui5-cb-item>
</ui5-combobox>

TBD

• backward compatibility
• eventing parameters
• form validation