Merge pull request #27972 from asmorkalov:as/dst_mat_type

Force empty output type where it's defined in API #27972

The PR replaces:
- https://github.com/opencv/opencv/pull/27936
- https://github.com/opencv/opencv/pull/21059

Empty matrix has undefined type, so user code should not relay on the output type, if it's empty. The PR introduces some exceptions:
- copyTo documentation defines, that the method re-create output buffer and set it's type.
- convertTo has output type as parameter and output type is defined and expected.

modules/core/src/copy.cpp

@@ -447,6 +447,7 @@ void Mat::copyTo( OutputArray _dst ) const
     if( empty() )
     {
         _dst.release();
+        _dst.create(size(), type());
         return;
     }