vim: Fix c when range ends in a multibyte character (#14139)

Release Notes:

- vim: Fixed `c <motion>` omitting trailing multibyte characters
([#13909](https://github.com/zed-industries/zed/issues/13909)).

crates/vim/test_data/test_find_multibyte.json

@@ -0,0 +1,7 @@
+{"Put":{"state":"<label for=\"guests\">ˇPočet hostů</label>"}}
+{"Key":"c"}
+{"Key":"t"}
+{"Key":"<"}
+{"Key":"o"}
+{"Key":"escape"}
+{"Get":{"state":"<label for=\"guests\">ˇo</label>","mode":"Normal"}}