Keyboard user cannot invoke Word's feature to convert MathType expression(s) to Office Math

[MathType test document.docx](https://github.com/user-attachments/files/25689092/MathType.test.document.docx)

As an AT user I want to convert MathType expressions in my Word document to Office Math. This is possible with modern versions of Word, but the feature appears to require a mouse click.

Steps to replicate:
- open the linked document in Word
- move to a MathType expression (hint - F11 and shift F11 will move forward and back between the objects)
- press F10 to invoke the context menu and nothing happens
- position the mouse pointer on the object
- activate right mouse button and the context menu is shown
- select `Object `and `Convert to Office Math`

Note: it is possible to for a screen reader user to route the mouse to the current object and simulate a mouse click, but this requires somewhat advanced knowledge. When selecting a MathType expression the screen reader may announce something like "graphic" or "selected, unselected".

See related issue #63