patch 8.1.0870: Vim doesn't use the new ConPTY support in Windows 10

Problem:    Vim doesn't use the new ConPTY support in Windows 10.
Solution:   Use ConPTY support, if available. (Nobuhiro Takasaki, closes #3794)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 374e701..fa7ed9b 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -6738,6 +6738,10 @@
 	else if (STRICMP(name, "terminal") == 0)
 	    n = terminal_enabled();
 #endif
+#if defined(FEAT_TERMINAL) && defined(WIN3264)
+	else if (STRICMP(name, "conpty") == 0)
+	    n = use_conpty();
+#endif
     }
 
     rettv->vval.v_number = n;