Spec for Improved keyboard handling in Conpty (microsoft#5887)

## Summary of the Pull Request

We have a number of bugs in the Terminal that all have the same singular root cause - VT input does not carry the same fidelity that Win32 input does. For Win32 applications there are certain keystrokes that simply cannot be represented with VT sequences. 

This is my proposal for how we'll handle all these cases. I'm proposing a _new VT sequence_, which will enable the Terminal to send input with all of the information that an `INPUT_RECORD` might have, to conpty. There, conpty will be able to send input to the client application with the same fidelity they're used to, enabling these keys to work for those applications once again. 

## PR Checklist
* [x] Specs microsoft#4999
* [x] I work here
* [x] is a spec

## Detailed Description of the Pull Request / Additional comments
_read the spec_

.github/actions/spell-check/dictionary/apis.txt

@@ -5,6 +5,7 @@ bitfields
 CLASSNOTAVAILABLE
 EXPCMDFLAGS
 EXPCMDSTATE
+fullkbd
 href
 IBox
 IBind

.github/actions/spell-check/expect/expect.txt

@@ -509,6 +509,7 @@ DECAWM
 DECCKM
 DECCOLM
 decf
+DECEKBD
 DECKPAM
 DECKPM
 DECKPNM
@@ -525,6 +526,7 @@ deconstructed
 DECPCTERM
 DECRC
 DECRLM
+DECRQM
 DECRST
 DECSASD
 DECSC
@@ -537,6 +539,7 @@ DECSEL
 DECSET
 DECSLRM
 DECSMBV
+DECSMKR
 DECSR
 decstandar
 DECSTBM
@@ -1163,6 +1166,7 @@ kcub
 kcud
 kcuf
 kcuu
+Kd
 keith
 kernelbase
 kernelbasestaging
@@ -1210,6 +1214,7 @@ LEFTSHIFT
 len
 lhs
 libpopcnt
+libtickit
 LIMITTEXT
 LINEDOWN
 LINESELECTION
@@ -1321,6 +1326,7 @@ MAKELONG
 MAKELPARAM
 MAKELRESULT
 malloc
+manpage
 MAPBITMAP
 MAPVIRTUALKEY
 MAPVK
@@ -1911,6 +1917,7 @@ REGSTR
 reingest
 Relayout
 RELBINPATH
+remoting
 renderengine
 rendersize
 reparenting

.github/actions/spell-check/expect/web.txt

@@ -4,5 +4,12 @@ www
 ecma
 rapidtables
 WCAG
+freedesktop
+ycombinator
+robertelder
+kovidgoyal
+leonerd
+fixterms
+uk
 winui
 appshellintegration