This commit introduces a small console-subsystem application whose sole
job is to consume TerminalConnection.dll and hook it up to something
other than Terminal. It is 99% of the way to a generic solution.
I've introduced a stopgap in TerminalPage that makes sure we launch
TerminalAzBridge using ConptyConnection instead of AzureConnection.
As a bonus, this commit includes a class whose sole job it is to make
reading VT input off a console handle not terrible. It returns you a
string and dispatches window size change callbacks.
Fixes#2267.
Fixes#4589.
Related to #2266 (since pwsh needs better VT).