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/proto/term.pro b/src/proto/term.pro
index 65e6740..147981c 100644
--- a/src/proto/term.pro
+++ b/src/proto/term.pro
@@ -64,6 +64,8 @@
 void del_termcode(char_u *name);
 void set_mouse_topline(win_T *wp);
 int check_termcode(int max_offset, char_u *buf, int bufsize, int *buflen);
+void term_get_fg_color(uint8_t *r, uint8_t *g, uint8_t *b);
+void term_get_bg_color(uint8_t *r, uint8_t *g, uint8_t *b);
 char_u *replace_termcodes(char_u *from, char_u **bufp, int from_part, int do_lt, int special);
 int find_term_bykeys(char_u *src);
 void show_termcodes(void);