patch 8.2.2344: using inclusive index for slice is not always desired

Problem:    Using inclusive index for slice is not always desired.
Solution:   Add the slice() method, which has an exclusive index. (closes
            #7408)
diff --git a/runtime/doc/usr_41.txt b/runtime/doc/usr_41.txt
index bac064c..5d4686a 100644
--- a/runtime/doc/usr_41.txt
+++ b/runtime/doc/usr_41.txt
@@ -619,6 +619,8 @@
 	submatch()		get a specific match in ":s" and substitute()
 	strpart()		get part of a string using byte index
 	strcharpart()		get part of a string using char index
+	slice()			take a slice of a string, using char index in
+				Vim9 script
 	strgetchar()		get character from a string using char index
 	expand()		expand special keywords
 	expandcmd()		expand a command like done for `:edit`
@@ -648,6 +650,7 @@
 	map()			change each List item
 	mapnew()		make a new List with changed items
 	reduce()		reduce a List to a value
+	slice()			take a slice of a List
 	sort()			sort a List
 	reverse()		reverse the order of a List
 	uniq()			remove copies of repeated adjacent items