patch 8.1.1823: command line history code is spread out

Problem:    Command line history code is spread out.
Solution:   Put the code in a new file. (Yegappan Lakshmanan, closes #4779)
            Also graduate the +cmdline_hist feature.
diff --git a/Filelist b/Filelist
index 0246ac7..9b0634d 100644
--- a/Filelist
+++ b/Filelist
@@ -23,6 +23,7 @@
 		src/change.c \
 		src/channel.c \
 		src/charset.c \
+		src/cmdhist.c \
 		src/crypt.c \
 		src/crypt_zip.c \
 		src/debugger.c \