patch 8.0.1743: terminal window options are named inconsistently

Problem:    Terminal window options are named inconsistently.
Solution:   prefix terminal window options with "termwin".  Keep the old names
            for now as an alias.
diff --git a/runtime/optwin.vim b/runtime/optwin.vim
index 128e92e..d36ddea 100644
--- a/runtime/optwin.vim
+++ b/runtime/optwin.vim
@@ -506,12 +506,15 @@
   call <SID>BinOptionL("crb")
 endif
 if has("terminal")
-  call append("$", "termsize\tsize of a terminal window")
+  call append("$", "termwinsize\tsize of a terminal window")
   call append("$", "\t(local to window)")
-  call <SID>OptionL("tms")
-  call append("$", "termkey\tkey that precedes Vim commands in a terminal window")
+  call <SID>OptionL("tws")
+  call append("$", "termwinkey\tkey that precedes Vim commands in a terminal window")
   call append("$", "\t(local to window)")
-  call <SID>OptionL("tk")
+  call <SID>OptionL("twk")
+  call append("$", "termwinscroll\tmax number of lines to keep for scrollback in a terminal window")
+  call append("$", "\t(local to window)")
+  call <SID>OptionL("twsl")
   if exists("&winptydll")
     call append("$", "winptydll\tname of the winpty dynamic library")
     call <SID>OptionG("winptydll", &winptydll)