Add support for opening the SecondaryToolbar on mousedown and enable triggering of its buttons on mouseup (issue 4810)

Even though this should work as requested, there might still be room for improvements of the code.
Fixes #4810.

Before we accept this PR, there are two questions that I believe that we need to ask ourselves.
* First of all, do we actually want this feature.
* Secondly, does this work properly on touch.