Also coerce unicode strings to FATE

This is mainly so that gajudesk can pass text box content to hz as-is,
but also allows users to pass utf8 binaries in, if they want to, for
some reason.

src/hz.erl

@@ -1850,6 +1850,18 @@ coerce({O, N, string}, Str, Direction) ->
     end;
 coerce({_, _, char}, Val, _Direction) when is_integer(Val) ->
     {ok, Val};
+coerce({O, N, char}, Str, to_fate) ->
+    Result = unicode:characters_to_list(Str),
+    case Result of
+        {error, _, _} ->
+            single_error({invalid, O, N, Str});
+        {incomplete, _, _} ->
+            single_error({invalid, O, N, Str});
+        [C] ->
+            {ok, C};
+        _ ->
+            single_error({invalid, O, N, Str})
+    end;
 coerce({O, N, {bytes, [Count]}}, Bytes, _Direction) when is_bitstring(Bytes) ->
     coerce_bytes(O, N, Count, Bytes);
 coerce({_, _, bits}, {bits, Num}, from_fate) ->
@@ -2546,6 +2558,12 @@ coerce_char_test() ->
     {ok, Type} = annotate_type(char, #{}),
     try_coerce(Type, $?, $?).
 
+coerce_unicode_test() ->
+    {ok, Type} = annotate_type(char, #{}),
+    % Latin Small Letter C with cedilla and acute
+    {ok, $ḉ} = coerce(Type, <<"ḉ"/utf8>>, to_fate),
+    ok.
+
 
 %%% Complex AACI paramter and namespace tests