SpecialRecentchanges: Don't use nonexistent messages for filter selector

Extensions can defined additional filters, but don't need to define
the corresponding messages. If they don't exist, just fall back to
'show' and 'hide'.

This also fixes the double-escaping of selector link contents and adds
missing entries to the list of messages used here.

Follow-up to Ibbfc3cd0.

Bug: 58449
Change-Id: Id323e3b7daced1e7b6b1e1add4e9e1bf7df05e4e