Radio group label does not provide accessible name

🐛 Bug Report

The radio group has a slot that a client can supply a label for. Providing a label does not set the accessible name for the radio group.
See this discussion thread for original context.

💻 Repro or Code Sample

<nimble-radio-group>
    <label slot="label">The Label</label>
   ...
</nimble-radio-group>

🤔 Expected Behavior

There should be some way to provide a label that automatically sets the accessible name for the group to the label provided.

😯 Current Behavior

The radio group has no accessible name.

💁 Possible Solution

We have reported this to FAST (https://github.com/microsoft/fast/issues/6360), and we even tried submitting a fix, but they did not accept it (https://github.com/microsoft/fast/pull/6367) for reasons they explain in the discussion.

🔦 Context

We were implementing the radio button/group and were trying to meet a11y expectations.