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/highlight.c b/src/highlight.c
index 7a32b22..77ad0bc 100644
--- a/src/highlight.c
+++ b/src/highlight.c
@@ -3753,6 +3753,11 @@
 
     need_highlight_changed = FALSE;
 
+#ifdef FEAT_TERMINAL
+    term_update_colors_all();
+    term_update_wincolor_all();
+#endif
+
     // Clear all attributes.
     for (hlf = 0; hlf < (int)HLF_COUNT; ++hlf)
 	highlight_attr[hlf] = 0;