* Make ConPTY build as both LIB and DLL.
* Update TerminalConnection reference to LIB version (because Terminal builds both UWP and Centennial, requiring different CRTs each).
* DLL is now available (and against desktop CRT) to be PInvokable from C# for WPF terminal.
Note, DLL MUST BUILD PRECOMP to get the magic pragma linking information to the Desktop CRT.
* don't audit PTY lib. I can't do safe things because the safe things we use don't fit back inside kernelbase.dll.
Closes#3563.