vim-patch:8.2.2606: strchars() defaults to counting composing characters

Problem:    strchars() defaults to counting composing characters.
Solution:   Add strcharlen() which ignores composing characters.

70ce8a1561

Use docs from latest Vim instead.

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/eval.lua

@@ -376,6 +376,7 @@ return {
     str2float={args=1, base=1},
     str2list={args={1, 2}, base=1},
     str2nr={args={1, 3}, base=1},
+    strcharlen={args=1, base=1},
     strcharpart={args={2, 3}, base=1},
     strchars={args={1, 2}, base=1},
     strdisplaywidth={args={1, 2}, base=1},