[Designer] Errors are shown when using templating expressions

Problem Description

If you are using a templated string as a property value within the designer, errors are displayed to the user.

Expected behavior

There should not be errors shown to the user if a property value is set to a templating expression.

Note: this does not impact functionality.

Card JSON

{
    "type": "AdaptiveCard",
    "$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
    "version": "1.5",
    "body": [
        {
            "type": "Container",
            "items": [
                {
                    "type": "TextBlock",
                    "text": "THIS IS A TEST ${priceChange}",
                    "wrap": true,
                    "color": "${if(priceChange >= 0, 'good', 'attention')}"
                }
            ]
        }
    ]
}

Data

{
    "priceChange": 4
}

Screenshot

Start in the Designer by reproducing the issue with the supplied Card JSON and data, focusing on the templated text and color properties. Confirm that the designer currently displays errors and that the card otherwise functions; done means those errors are no longer shown for templating expressions.