Force activate existing windows when running a commandline in them

[zadjii-msft]

This will make sure to summon the terminal window when running a
commandline in it.

• If the window is on another desktop, the OS will switch to the desktop
  the window is on.
• If the window is minimized, it will restore it.

This is taken from my quake mode branch. It works aggressively. 848682a,
fee6473, 342d3f2, 5052d31 all had other attempts at doing this, but they
didn't work reliably. Part of the trick is that I don't think Windows
wants one process to be able to move another process into the
foreground. In this case though, we do want to move ourself into the
foreground, and this AttachThreadInput hack seems to be the only way
to do it reliably.

References #5000
Uses code authored for #653

Closes https://github.com/microsoft/terminal/projects/5#card-54636373

[DHowett]

Horrified that this works. Wow.

[ghost]

Hello @DHowett!

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[ghost]

🎉Windows Terminal Preview v1.7.572.0 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes
• Store Download