Rework the text to numeric conversion routines so that they work with either

UTF8 or UTF16 and do not require a NULL terminator.  This allowed text to
numeric conversion without reallocating the string.

FossilOrigin-Name: 14eed3a0e0a45c6f2904a3a134aa27c159916f7b

src/func.c

@@ -285,7 +285,7 @@ static void roundFunc(sqlite3_context *context, int argc, sqlite3_value **argv){
       sqlite3_result_error_nomem(context);
       return;
     }
-    sqlite3AtoF(zBuf, &r);
+    sqlite3AtoF(zBuf, &r, sqlite3Strlen30(zBuf), SQLITE_UTF8);
     sqlite3_free(zBuf);
   }
   sqlite3_result_double(context, r);