Prevent the creation of invalid MWInternalLinks

By testing against a regex of legal title characters we can determine
if the entered text is a valid internal link. If it isn't we should
prevent the link inpsector from creating/changing the annotation.

Bug: 33094
Change-Id: Ia1df602601e4e82fc351279e432c28c425f5157a
Merge "Prevent the creation of invalid MWInternalLinks"