Add a spec for an In-process ConPTY (#17387)

👉 Preview:
https://github.com/microsoft/terminal/blob/dev/lhecker/13000-spec/doc/specs/%2313000%20-%20In-process%20ConPTY.md

The spec has a tl;dr! The tl;dr^2 for the commit message:
* Less bugs
* Less code
* More perf

.github/actions/spelling/expect/expect.txt

@@ -1237,6 +1237,7 @@ NUMSCROLL
 NUnit
 nupkg
 NVIDIA
+NVT
 OACR
 objbase
 ocolor
@@ -1411,6 +1412,7 @@ processenv
 processhost
 PROCESSINFOCLASS
 PRODEXT
+Productize
 PROPERTYID
 PROPERTYKEY
 propertyval
@@ -1818,6 +1820,7 @@ TITLEISLINKNAME
 TJson
 TLambda
 TLDP
+tldr
 TLEN
 TMAE
 TMPF