Important context: To make a window smaller programmatically,
the win32 console APIs have since forever required you to

• narrow the viewport
• then narrow the buffer

To make the window larger you had to

• enlarge the buffer
• then enlarge the viewport

This is because a viewport had to fit into the buffer and vice versa.
ConEmu was very popular in the past and used this to implement proper
terminals around conhost. When WSL came along this resulted in a
problem: It wants SIGWINCH-style notifications. And there are none
on Windows. A long time ago, a hack was introduced that simply
raised buffer size events on any viewport size changes.

The problem: It was raised for any viewport size changes.
And it was also raised for ASB switching.

Problema numero due: OpenSSH for WIndows is like WSL, but it has a
severe bug: A SIGWINCH during a partial input read will corrupt the
read and the other side will read either garbage or duplicate input.

Well, we can fix that by just not raising buffer size events.
It's very dangerous, because it may easily regress ConEmu (etc.).

See: PowerShell/Win32-OpenSSH#2275

Also: Fun fact, we've been ignoring ENABLE_WINDOW_INPUT
since Windows 1607! No way fixing this breaks anything! /s

So, this PR introduces two regressions:

• ENABLE_WINDOW_INPUT is being respected again
• WINDOW_BUFFER_SIZE_EVENT is not sent anymore
  when the viewport changes if VT mode disabled

Changes:

• Reintroduce support for ENABLE_WINDOW_INPUT
• Coalesce buffer size events
• Avoid such events when switching ASB on/off
• Ensure we reliably raise the events for viewport size changes

This is part of #281.

Validation Steps Performed

• Spawn OpenConsole
• Run ConEmuC64.exe -AUTOATTACH -GHWND=NEW
• Run wsl -- bash
• Run while stty size; do read -rt .05 ||:; done
• Narrowing the window reduces the WSL width ✅
• Widening the window increases the WSL width ✅