patch 8.0.0283: mode() does not indicate Insert mode completion

Problem:    The return value of mode() does not indicate that completion is
            active in Replace and Insert mode. (Zhen-Huan (Kenny) Hu)
Solution:   Add "c" or "x" for two kinds of completion. (Yegappan Lakshmanan,
            closes #1397)  Test some more modes.
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 58a61f2..1b3f112 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -5848,9 +5848,13 @@
 			S	Select by line
 			CTRL-S	Select blockwise
 			i	Insert
+			ic	Insert mode completion |compl-generic|
+			ix	Insert mode |i_CTRL-X| completion
 			R	Replace |R|
+			Rc	Replace mode completion |compl-generic|
 			Rv	Virtual Replace |gR|
-			c	Command-line
+			Rx	Replace mode |i_CTRL-X| completion
+			c	Command-line editing
 			cv	Vim Ex mode |gQ|
 			ce	Normal Ex mode |Q|
 			r	Hit-enter prompt