fix(Combobox): add event propagation to mouse down

[dakahn]

Closes #9073

• removes event.stopPropagation() from the onMouseUp event on the toggle button's props.
• onMouseUp on the toggle button now moves active focus to the text input

Testing / Reviewing

• go into ../ComboBox-story.js and duplicate the <ComboBox> seen on line 65 like so
  
• open the second ComboBox's listbox either by clicking the text input or the toggle button
• click the first ComboBox's toggle button and observe the second Combobox's listbox close as expected

Notes

@joshblack pretty sure stopping event propagation was critical for some reason we're missing here -- do you remember why?

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[tw15egan]

Working as expected 👍🏻 ✅

[tay1orjones]

I debugged this at length with @sstrubberg today, and it seems just scoping the event.stopPropogation to only when the listbox isOpen fixes everything. I can no longer get two listboxes to be open at the same time, and the bug @joshblack pointed out on the single combobox is also fixed.

only.one.open.at.a.time.mov

I added a multipleInstances story to demo this. I can take it out, but sort of feel it's nice to have and we could leave in? I'm good either way.

[tw15egan]

Re-reviewed and removed the test story, LGTM 👍🏻