Properly filter focus events from the console API

[lhecker]

This is an improved fix for #13238. Instead of handling focus events in
the TerminalInput::HandleKey function and the need to filter them
out depending on where they came from, we simply don't call HandleKey
in the first place. This makes the somewhat unreliable CameFromApi
function unnecessary and the code a bit more robust.

This change is required because CameFromApi is not representable
in a INPUT_RECORD and I'm getting rid of IInputEvent.

Validation Steps Performed

• No [O when exiting nvim ✅
• Mouse input in nvim works ✅

[DHowett]

lmao, FAIL_FAST_IF inside a try{}