patch 8.0.1362: terminal window colors wrong when using Terminal highlighting

Problem:    Terminal window colors wrong when using Terminal highlighting.
Solution:   Set ansi_index when setting the default color.  Also cache the
            color index for Terminal. (Ozaki Kiichi, closes #2393)
diff --git a/src/proto/terminal.pro b/src/proto/terminal.pro
index 7f64b90..4b39daa 100644
--- a/src/proto/terminal.pro
+++ b/src/proto/terminal.pro
@@ -20,6 +20,7 @@
 int term_get_attr(buf_T *buf, linenr_T lnum, int col);
 char_u *term_get_status_text(term_T *term);
 int set_ref_in_term(int copyID);
+void set_terminal_default_colors(int cterm_fg, int cterm_bg);
 void f_term_getaltscreen(typval_T *argvars, typval_T *rettv);
 void f_term_getattr(typval_T *argvars, typval_T *rettv);
 void f_term_getcursor(typval_T *argvars, typval_T *rettv);