Introduction of menus in Zircon

[coldwarrl]

Introduction of menus in Zircon

Improved behavior

Many complex text based UIs feature menus (with a menu bar) and it might also be a valuable GUI widget in Zircon (e.g. for customizing views, switching overlay etc.). Also mnemonics might be introduced.

Suggested way of achieving the improvement

Comments from @adam-arold
"drop down menus
this can be done when we have the new layering architecture
what we discussed before
the dropdown can be a modal
which cancels itself if you click outside of its bounding box
as opposed to a dialog which will not
we can even do this fancy shadow thing
with transparency"

[adam-arold]

Great idea! I'll add this to the next release!