patch 8.2.2606: strchars() defaults to counting composing characters

Problem:    strchars() defaults to counting composing characters.
Solution:   Add strcharlen() which ignores composing characters.
diff --git a/runtime/doc/usr_41.txt b/runtime/doc/usr_41.txt
index 8113bef..0d17298 100644
--- a/runtime/doc/usr_41.txt
+++ b/runtime/doc/usr_41.txt
@@ -611,7 +611,8 @@
 	stridx()		first index of a short string in a long string
 	strridx()		last index of a short string in a long string
 	strlen()		length of a string in bytes
-	strchars()		length of a string in characters
+	strcharlen()		length of a string in characters
+	strchars()		number of characters in a string
 	strwidth()		size of string when displayed
 	strdisplaywidth()	size of string when displayed, deals with tabs
 	setcellwidths()		set character cell width overrides