[Authoring] Missing Icon Card element from JSONSchema

Target Application

Teams

Application Operating System

Other

Schema Version

1.5

Problem Description

Adaptive cards editor in Teams dev portal propose Icon element but is nowhere to be found in jsonschema.
Therefore I can't use schema validation for cards using Icon element

Expected Outcome

Being able to validate cards with Icon element against adaptive card schema 1.5

Actual Outcome

Validation fails with https://adaptivecards.io/schemas/1.5.0/adaptive-card.json but renders perfectly on teams

Card JSON

{
    "type": "AdaptiveCard",
    "$schema": "https://adaptivecards.io/schemas/adaptive-card.json",
    "version": "1.5",
    "body": [
        {
            "type": "Icon",
            "name": "AddCircle"
        }
    ]
}

Repro Steps

No response

Start by comparing the Adaptive Cards 1.5 schema at the linked URL with the Icon element shown in the issue's card JSON. Confirm how the schema currently rejects that element; done means the same card validates successfully against the 1.5 schema.