patch 8.1.1727: code for viminfo support is spread out

Problem:    Code for viminfo support is spread out.
Solution:   Move to code to viminfo.c. (Yegappan Lakshmanan, closes #4686)
diff --git a/src/proto.h b/src/proto.h
index e854546..cc1c8fb 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -107,6 +107,9 @@
 # ifdef FEAT_ARABIC
 #  include "arabic.pro"
 # endif
+# ifdef FEAT_VIMINFO
+# include "viminfo.pro"
+# endif
 
 /* These prototypes cannot be produced automatically. */
 int smsg(const char *, ...)