Support official ApexDocs format.

In Winter 26, Salesforce has formalized and documented the official ApexDoc syntax and tags.

This issue is to review the documentation and update the ApexDocs tool to match the official syntax.

https://help.salesforce.com/s/articleView?id=release-notes.rn_apex_apexdoc.htm&release=258&type=5

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_doc_intro.htm