Fix missing window border when use "win+arrow down" in fullscreen mode in Terminal

[serd2011]

Window sends an event that requests exit from fullscreen then SC_RESTORE messages is sent and it is in fullscreen mode.
Closes #10607

Validation Steps Performed

Border and tabbar now appear after exiting fullscreen via "win+arrow down".

[zadjii-msft]

Wild. Makes sense to me. Thanks for doing this!

[DHowett]

This PR only fixes Terminal, not conhost. Should open new issue for conhost or add stage for this one.

If you want to send another PR, that would be best! Conhost changes are easier to review in isolation :)

[DHowett]

This is great. Thank you!

[ghost]

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[krzysdz]

This PR causes build errors, because, when combined with #11404, WM_SYSCOMMAND case value is used twice. The problem is here (lines 609 and 623):

terminal/src/cascadia/WindowsTerminal/IslandWindow.cpp

Lines 609 to 631 in 7aae2e9

	case WM_SYSCOMMAND:
	{
	if (wparam == SC_RESTORE && _fullscreen)
	{
	_ShouldExitFullscreenHandlers();
	return 0;
	}
	break;
	}
	case WM_MENUCOMMAND:
	{
	_NotifyNotificationIconMenuItemSelectedHandlers((HMENU)lparam, (UINT)wparam);
	return 0;
	}
	case WM_SYSCOMMAND:
	{
	auto search = _systemMenuItems.find(LOWORD(wparam));
	if (search != _systemMenuItems.end())
	{
	search->second.callback();
	}
	break;
	}

[ghost]

🎉Windows Terminal Preview v1.12.3472.0 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes
• Store Download

[ghost]

🎉Windows Terminal v1.11.3471.0 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes
• Store Download