Merge pull request #21553 from VadimLevin:dev/vlevin/scope-for-classes-4x-port

4.x: submodule or a class scope for exported classes

* feature: submodule or a class scope for exported classes

All classes are registered in the scope that corresponds to C++
namespace or exported class.

Example:
`cv::ml::Boost` is exported as `cv.ml.Boost`
`cv::SimpleBlobDetector::Params` is exported as
`cv.SimpleBlobDetector.Params`

For backward compatibility all classes are registered in the global
module with their mangling name containing scope information.
Example:
`cv::ml::Boost` has `cv.ml_Boost` alias to `cv.ml.Boost` type

* refactor: remove redundant GAPI aliases

* fix: use explicit string literals in CVPY_TYPE macro

* fix: add handling for class aliases

modules/gapi/misc/python/package/gapi/__init__.py

@@ -287,15 +287,4 @@ def kernel(op_cls):
     return kernel_with_params
 
 
-# FIXME: On the c++ side every class is placed in cv2 module.
-cv.gapi.wip.draw.Rect = cv.gapi_wip_draw_Rect
-cv.gapi.wip.draw.Text = cv.gapi_wip_draw_Text
-cv.gapi.wip.draw.Circle = cv.gapi_wip_draw_Circle
-cv.gapi.wip.draw.Line = cv.gapi_wip_draw_Line
-cv.gapi.wip.draw.Mosaic = cv.gapi_wip_draw_Mosaic
-cv.gapi.wip.draw.Image = cv.gapi_wip_draw_Image
-cv.gapi.wip.draw.Poly = cv.gapi_wip_draw_Poly
-
-cv.gapi.streaming.queue_capacity = cv.gapi_streaming_queue_capacity
-
 cv.gapi.wip.GStreamerPipeline = cv.gapi_wip_gst_GStreamerPipeline