patch 8.0.1194: actual fg and bg colors of terminal are unknown

Problem:    Actual fg and bg colors of terminal are unknown.
Solution:   Add t_RF.  Store response to t_RB and t_RF, use for terminal.
diff --git a/src/vim.h b/src/vim.h
index 4567c36..11b7b08 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -1998,11 +1998,12 @@
 #define VV_TYPE_NONE	78
 #define VV_TYPE_JOB	79
 #define VV_TYPE_CHANNEL	80
-#define VV_TERMRGBRESP	81
-#define VV_TERMU7RESP	82
-#define VV_TERMSTYLERESP 83
-#define VV_TERMBLINKRESP 84
-#define VV_LEN		85	/* number of v: vars */
+#define VV_TERMRFGRESP	81
+#define VV_TERMRBGRESP	82
+#define VV_TERMU7RESP	83
+#define VV_TERMSTYLERESP 84
+#define VV_TERMBLINKRESP 85
+#define VV_LEN		86	/* number of v: vars */
 
 /* used for v_number in VAR_SPECIAL */
 #define VVAL_FALSE	0L