dnn: Support more operators in CANN backend

[fengyuentau]

This PR adds the support of following layers:

• Sub
• PRelu
• DeConv
• Also warn users if backend is switched back to default if some of the layers are not supported.
• [Dropped] LSTM: some hacks (adding layers) were introduced which makes it even harder to build the graph for CANN backend.

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

[asmorkalov]

Buildbot reports documentation warning:

/build/precommit_docs/4.x/opencv/modules/dnn/include/opencv2/dnn/dnn.hpp:353: warning: The following parameters of cv::dnn::Layer::initCann(const std::vector< Ptr< BackendWrapper > > &inputsWrapper, const std::vector< Ptr< BackendWrapper > > &outputsWrapper, const std::vector< Ptr< BackendNode > > &nodes) are not documented:

[fengyuentau]

Buildbot reports documentation warning:

Thank you for the reminder. I will add the documentation in the next commit.

[fengyuentau]

Buildbot reports documentation warning:

/build/precommit_docs/4.x/opencv/modules/dnn/include/opencv2/dnn/dnn.hpp:353: warning: The following parameters of cv::dnn::Layer::initCann(const std::vector< Ptr< BackendWrapper > > &inputsWrapper, const std::vector< Ptr< BackendWrapper > > &outputsWrapper, const std::vector< Ptr< BackendNode > > &nodes) are not documented:

Resolved.