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/src/testdir/test_utf8.vim b/src/testdir/test_utf8.vim
index a5fd4fb..5454e43 100644
--- a/src/testdir/test_utf8.vim
+++ b/src/testdir/test_utf8.vim
@@ -11,7 +11,7 @@
   bwipeout!
 endfunc
 
-" Test for built-in function strchars()
+" Test for built-in functions strchars() and strcharlen()
 func Test_strchars()
   let inp = ["a", "あいa", "A\u20dd", "A\u20dd\u20dd", "\u20dd"]
   let exp = [[1, 1, 1], [3, 3, 3], [2, 2, 1], [3, 3, 1], [1, 1, 1]]
@@ -20,6 +20,13 @@
     call assert_equal(exp[i][1], inp[i]->strchars(0))
     call assert_equal(exp[i][2], strchars(inp[i], 1))
   endfor
+
+  let exp = [1, 3, 1, 1, 1]
+  for i in range(len(inp))
+    call assert_equal(exp[i], inp[i]->strcharlen())
+    call assert_equal(exp[i], strcharlen(inp[i]))
+  endfor
+
   call assert_fails("let v=strchars('abc', [])", 'E745:')
   call assert_fails("let v=strchars('abc', 2)", 'E1023:')
 endfunc