`m.topic` field of `m.room.topic` has wrong format

[zecakeh]

The JS SDK expects this format:

{
    "topic": "All about **pizza**",
    "m.topic": [{
        "body": "All about **pizza**",
        "mimetype": "text/plain",
    }, {
        "body": "All about <b>pizza</b>",
        "mimetype": "text/html",
    }],
}

But the actual format defined in the spec and MSC3765 is:

{
    "topic": "All about **pizza**",
    "m.topic": {
        "m.text": [{
            "body": "All about **pizza**",
            "mimetype": "text/plain",
        }, {
            "body": "All about <b>pizza</b>",
            "mimetype": "text/html",
        }],
    }
}

To clarify, currently the SDK expects m.topic to be an array of objects, but m.topic should be an object with an m.text field that is an array of objects.

[dbkr]

Tricky one to triage as it really sucks but is mostly an interoperability bug... I've gone with 'occasional'. Also, we will probably have to do migration here otherwise any rooms with links etc. will sprout random markdown syntax as they fall back to the old style 🤦