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/window.c b/src/window.c
index 3f99681..d28962a 100644
--- a/src/window.c
+++ b/src/window.c
@@ -1422,6 +1422,9 @@
 #ifdef FEAT_SYN_HL
     check_colorcolumn(newp);
 #endif
+#ifdef FEAT_TERMINAL
+    term_update_wincolor(newp);
+#endif
 }
 
 /*
@@ -3684,6 +3687,9 @@
 #if defined(FEAT_SYN_HL) || defined(FEAT_SPELL)
     wp->w_s = &wp->w_buffer->b_s;
 #endif
+#ifdef FEAT_TERMINAL
+    term_reset_wincolor(wp);
+#endif
 }
 
 /*