patch 8.2.3628: looking terminal colors is a bit slow

Problem:    Looking terminal colors is a bit slow.
Solution:   Cache the terminal colors. (closes #9130, closes #9058)
diff --git a/src/proto/terminal.pro b/src/proto/terminal.pro
index f5e3258..9304606 100644
--- a/src/proto/terminal.pro
+++ b/src/proto/terminal.pro
@@ -28,7 +28,9 @@
 int term_show_buffer(buf_T *buf);
 void term_change_in_curbuf(void);
 int term_get_attr(win_T *wp, linenr_T lnum, int col);
-void term_update_colors(term_T *term);
+void term_reset_wincolor(win_T *wp);
+void term_update_wincolor(win_T *wp);
+void term_update_wincolor_all(void);
 void term_update_colors_all(void);
 char_u *term_get_status_text(term_T *term);
 void term_clear_status_text(term_T *term);