patch 8.2.4617: no completion for :scriptnames

Problem:    No completion for :scriptnames.
Solution:   Implement :scriptnames completion. (Yegappan Lakshmanan,
            closes #10005)
diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 602d909..2d615c5 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -3256,6 +3256,7 @@
 		messages	|:messages| suboptions
 		option		options
 		packadd		optional package |pack-add| names
+		scriptnames	sourced script names |:scriptnames|
 		shellcmd	Shell command
 		sign		|:sign| suboptions
 		syntax		syntax file names |'syntax'|
@@ -3275,7 +3276,10 @@
 
 		If the 'wildoptions' option contains 'fuzzy', then fuzzy
 		matching is used to get the completion matches. Otherwise
-		regular expression matching is used.
+		regular expression matching is used.  Thus this function
+		follows the user preference, what happens on the command line.
+		If you do not want this you can make 'wildoptions' empty
+		before calling getcompletion() and restore it afterwards.
 
 		If {type} is "cmdline", then the |cmdline-completion| result is
 		returned.  For example, to complete the possible values after