Fix alt+space opening system menu and sending keys to terminal

[PankajBhojwani]

If both of the following are true

1. alt+space is not explicitly unbound
2. alt+space is not bound to a command

Then the window procedure will handle the alt+space to open up the context menu.
In this case, we need to make sure we don't send the keys to terminal.

Closes #10935

[lhecker]

Isn't this equal to having a default key binding for Alt+Space which is bound to a no-op action?

[DHowett]

Here's a really silly thought. What if we just add a new "openSystemMenu" binding? We could be done with this whole issue and allow people to re-bind it to whatever they want! All we'd need to do is move _OpenSystemMenu to IslandWindow, hook up some events from AppHost/AppLogic/TerminalPage (ugh hopefully not all of them) and... we're off to the races! We can also do that work later and mark this part with a big TODO that links to a workitem that says what I just said above^

[DHowett]

Perhaps there's a nod to #5833 somewhere in there... but that is a CONSOLE workitem. Hm.

[zadjii-msft]

What if we just add a new "openSystemMenu" binding? We could be done with this whole issue and allow people to re-bind it to whatever they want!

that's a good idea

[PankajBhojwani]

Here's a really silly thought. What if we just add a new "openSystemMenu" binding? We could be done with this whole issue and allow people to re-bind it to whatever they want! All we'd need to do is move _OpenSystemMenu to IslandWindow, hook up some events from AppHost/AppLogic/TerminalPage (ugh hopefully not all of them) and... we're off to the races! We can also do that work later and mark this part with a big TODO that links to a workitem that says what I just said above^

Sounds good to me! Added a work item for it for 1.12

[ghost]

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[DHowett]

I am okay with this solution -- it's targeted and specific, but it does rely on explicit unbinding. I don't love that, but it's better than the alternative.

Piping input directly into the terminal using one of the direct input listeners is always going to be fraught with peril.

@PankajBhojwani, alt+space works for the menu when you do this? Excellent.

[zadjii-msft]

Okay yea lets do this for now, but openSystemMenu is definitely the better solution here long-term