patch 8.1.1927: code for dealing with script files is spread out

Problem:    Code for dealing with script files is spread out.
Solution:   Move the code to scriptfile.c. (Yegappan Lakshmanan, closes #4861)
diff --git a/src/proto.h b/src/proto.h
index 3b6d1ac..10c8ff5 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -184,6 +184,7 @@
 #  include "quickfix.pro"
 # endif
 # include "regexp.pro"
+# include "scriptfile.pro"
 # include "screen.pro"
 # include "session.pro"
 # if defined(FEAT_CRYPT) || defined(FEAT_PERSISTENT_UNDO)