Update displaytitle on save (try #3)

Parse the wikitext we already have.

This is mostly a revert of commit f84b880a548d0d1e35e68699e8aac5d28fe6cdb4.

Bug: 50341
Change-Id: I312bafb0e7d61b0abd42d6ca7ea2e4b5dcdc61be
Merge "Update displaytitle on save (try #3)"