Implement XEP-0106: JID Escaping

When mapping Matrix rooms to XMPP, certain characters are not valid in JIDs and must be escaped. The default mechanism for that is [XEP-0106](https://xmpp.org/extensions/xep-0106.html), which also provides a list of which characters to escape:

- U+0022 (")
- U+0026 (&)
- U+0027 (')
- U+002F (/)
- U+003A (:)
- U+003C (<)
- U+003E (>)
- U+0040 (@)

Please convert those into the respective escaped hexadecimal notation, i.e. `"` --> `\22`

Start by locating the Matrix-to-XMPP JID mapping entry point in the repository. Implement XEP-0106 escaping for the eight characters listed in the issue, using their hexadecimal forms, and verify that mapped JIDs contain the expected escaped values. An open linked pull request indicates that this work is already underway.

Written by the indexing model from the issue text.