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/eval.c b/src/eval.c
index 8670e12..d4fba7f 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -187,7 +187,8 @@
     {VV_NAME("t_none",		 VAR_NUMBER), VV_RO},
     {VV_NAME("t_job",		 VAR_NUMBER), VV_RO},
     {VV_NAME("t_channel",	 VAR_NUMBER), VV_RO},
-    {VV_NAME("termrgbresp",	 VAR_STRING), VV_RO},
+    {VV_NAME("termrfgresp",	 VAR_STRING), VV_RO},
+    {VV_NAME("termrbgresp",	 VAR_STRING), VV_RO},
     {VV_NAME("termu7resp",	 VAR_STRING), VV_RO},
     {VV_NAME("termstyleresp",	VAR_STRING), VV_RO},
     {VV_NAME("termblinkresp",	VAR_STRING), VV_RO},