conpty: request DSR-CPR before Win32 input mode

[DHowett]

This prevents an issue in conhost where older versions of Windows Terminal (including the ones currently inbox in Windows, as well as stable and preview) will still cause WSL interop to hang on startup.

Since VT input is erroneously re-encoded as Win32 input events on those versions, we need to make sure we request the cursor position before enabling Win32 input mode. That way, the CPR we get back is properly encoded.

[DHowett]

From #16408

For this to be of any benefit, your proposed fix would assumedly have to make its way into the inbox conhost before Terminal Stable gets the #16407 fix. Am I understanding that correctly?

If that's a likely scenario, then it probably is worth doing. The only downside I can see is if the CPR response is slow, it might be possible that some keypresses arrive in VT format before win32-input mode kicks in. But that doesn't seem like a massive issue, assuming it's even possible at all.
@j4james, #14608

That's exactly it - we haven't even begun updating WT 1.18 and 1.19 in the store to fix this, but the conhost changes are making their way up out through the insider program. It's a narrow window where it'll be ~ ~ weird ~ ~, but this makes it smaller.

Good call about there being VT input in the wrong format on startup. It's probably safe - applications will hopefully not be expecting to receive raw modifier keypresses (🤞🏻) that early on . . .

[lhecker]

Thanks for doing this!

[zadjii-msft]

well yea this is obvious in retrospect