Feature summary (what you would like to be able to do and where):
When editing MediaWiki:BlockedExternalDomains.json via the special page Special:BlockedExternalDomains, if the magic test for signature or timestamp is included in the notes section, it should be parsed and included in the edit

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
Steps to discover:

1. Go to Special:BlockedExternalDomains
2. Enter a domain
3. Enter a note and ~~~~
4. Submit
5. Notice that the literal signature magic word is stored instead of being parsed

Use case is to allow the json page to be self-documenting for editors that include their information

Benefits (why should this be implemented?):
Other wikitext is working here, this would allow a consistent editing experience

I think this USED to work and has since broken. May be a good workaround pending a possible design change requested in T341626