Escape group names in selectors

[thecrypticace]

In v3.2.4 we would hard crash on the group variant group/${id}. This is because the name ${id}:

1. Had { and } in it
2. These were unescaped
3. Even if manually escaped, we weren't handling this properly.

Here we fix this by doing two things:

1. Escaping the group / peer names so they can appear in a selector un-modified.
2. Handling escaped characters properly in a variant format string

Fixes #10266