JavaScript library does not natively support markdown, and third-party libs are too permissive

This sample has a lot of markdown syntax that shouldn’t be supported according to the docs.

{
    "$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
    "type": "AdaptiveCard",
    "version": "1.0",
    "body": [
        {
            "type": "TextBlock",
            "text": "## Markdown Headers should not be supported"
        },
        {
            "type": "TextBlock",
            "text": "___"
        },
        {
            "type": "TextBlock",
            "text": "Neither should horizontal rules"
        },
        {
            "type": "TextBlock",
            "text": "Some of my spaces are being eaten up by the         markdown parser"
        },
        {
            "type": "TextBlock",
            "text": "~~Strikethrough should not be supported.~~"
        },
        {
            "type": "TextBlock",
            "text": ">Quote blocks should be ignored"
        },
        {
            "type": "TextBlock",
            "text": "Markdown | Tables | Work\n:--- | :---: | ---:\n*And* | change | **horizontal alignment**\n1 | 2 | 3"
        },
        {
            "type": "TextBlock",
            "text": "    This one I don't really understand"
        },
        {
            "type": "TextBlock",
            "text": "````\nBut Seems to be a shortcut for code blocks, which should be ignored."
        }
    ]
}

Renders as:

[Surezt22]

@Vasanth-S / @matthidinger This is the markdown parser we are using for our react-native implementation. Currently, it supports the below 5 types:

• Bold
• Italic
• Ordered List
• Unordered List
• Link

You can refer the same to support web-based markdown processor. In case, if you need any help, we are happy to work on that.

[jonmill]

Tracked by #1984