Replace hacky wikitext warning listener with sequences

Uses the generic sequence detection now available in core instead
of a custom hack that had to been manually bound and unbound to
every surface and surface widget.

As the sequence detection looks at just-typed characters the behaviour
has reverted to showing a auto-hide message. This resolves an issue
with the previous system whereby typing in the same paragraph as existing
wikitext patterns triggered the warning.

Depends on I6a4d71d in core.

Bug: T53751
Change-Id: I7d914b1b60a1cf8c79a724e5f634e1e666c9562d
Register '<p># ' sequence for creating numbered lists

Replaces wikitext warning sequence.

Change-Id: I438654212284d4a022b11bd59ea2f8bc52f0d737