[HTML] Add isPrimary boolean property to the Action class

Problem

For backwards compatibility with its previous Actionable Message card format, Outlook needs the ability to mark an action as “primary” so that it can get a different visual treatment.

Solution

In the HTML renderer:

• Introduce an isPrimary boolean property on the Action class
• Introduce a way to custom parse Action objects (similarly to the custom parsing of Element objects)

Design

New isPrimary property on the Action class:

export class Action {
    ...
    isPrimary: boolean = false;
    ...
}

Custom action parsing events (global and per-card, like other events):

export class AdaptiveCard {
    ...
    static onParseAction: (action: Action, json: any) => void = null;
    onParseAction: (action: Action, json: any) => void = null;
    ...
}

It is the responsibility of the host to handle the onParseAction event to custom parse the isPrimary action. isPrimary is not parsed out of the box and is not an official Adaptive property.

[dclaux]

Yes, we can do that. I just opened https://github.com/Microsoft/AdaptiveCards/issues/1517

[dptejas]

Implemented solution in #1521