patch 9.1.1391: Vim does not have a vertical tabpanel

Problem:  Vim does not have a tabpanel
Solution: include the tabpanel feature
          (Naruhiko Nishino, thinca)

closes: #17263

Co-authored-by: thinca <thinca@gmail.com>
Signed-off-by: Naruhiko Nishino <naru123456789@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 74afd9d..76955a7 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -7415,6 +7415,13 @@
 		0
 #endif
 		},
+	{"tabpanel",
+#if defined(FEAT_TABPANEL)
+		1,
+#else
+		0,
+#endif
+	},
 	{"tag_binary", 1},	// graduated feature
 	{"tcl",
 #if defined(FEAT_TCL) && !defined(DYNAMIC_TCL)