Add the \todo and \missingfigure commands from the todonotes package to the todo tool window.

[slideclimb]

Fix #3673

Summary of additions and changes

• Added the \todo and \missingfigure commands from the todonotes package to the todo tool window.

Some remarks on limitations and the implementation:

• The \todo commands are counted twice in the total todo count for a file/project/etc because it matches both the new \todo and the existing todo patterns. We have more control on what appears in the tree, so it only appears once there.
• According to the dev guide the EP to register these extra places is indexPatternSearch, but the only way seems to be using quite some internal api's. So no guarantees that this keeps working properly in the future.
• The commands are not highlighted as todo items and are not customisable via the todo settings, as that is currently not possible (see IJPL-172245). Once this is fixed, we can probably change our implementation to only include the Searcher?

How to test this pull request

% todo testaqi
\todo{test}

\missingfigure{test}

• Updated the documentation, or no update necessary
• Added tests, or no tests necessary

[PHPirates]

So if a user wants the editor highlighting of \todo's and correct information in the tool window, then the user needs to add a pattern for \todo and then use a filter to filter only on the default and the new \todo pattern?
I think that is nontrivial and should be added to our user documentation.