igxCombo API changes - value & selection

[Lipata]

Description

• igxCombo value should return an array of value keys instead of display keys
• igxCombo selection should return an array of data items. Currently, it does it, when valueKey is not provided, but return array of value keys when the valueKey is provided, which should be done by the value property.
• new displayValue that will return [] of display keys or CSV.
• values in the events should be synced with igc-combo: Combo change event emits wrong value igniteui-webcomponents#796

Please check the latest API changes in the spec: https://github.com/IgniteUI/igniteui-angular/wiki/IgxCombo-(Component)

Please check the web-components combo spec and implementation in order to be in sync between 2 frameworks: https://github.com/IgniteUI/igniteui-webcomponents/wiki/%5BWIP%5D-Combo-Specification

Migrations will be needed.

• igniteui-angular version: 16.x