dnn: cleanup of tengine backend #24122🚀 Cleanup for OpenCV 5.0. Tengine backend is added for convolution layer speedup on ARM CPUs, but it is not maintained and the convolution layer on our default backend has reached similar performance to that of Tengine.
Tengine backend related PRs:
- https://github.com/opencv/opencv/pull/16724
- https://github.com/opencv/opencv/pull/18323
### Pull Request Readiness Checklist
See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request
- [x] I agree to contribute to the project under Apache 2 License.
- [x] 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
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake
Support downloading 3rdparty resources from Gitcode & Gitlab-style mirrors
* replace github.com with gitcode.net for ocv_download
* replace raw.githubusercontent.com with gitcode.net for ocv_download
* rename funtions and remove some comments
* add options for custom mirrors, which simply replace domain github.com & githubusercontent.com
* run ocv_init_download once; replace DL_URL with mirrored one when calling ocv_download
* fix for empty download links when not using mirror
* fix bugs: set(.. .. PARENT_SCOPE) for ocv_init_download; correct macro names for replace github archives and raw githubusercontent
* adjusted mirror swapping impl: replace with mirrored link before each ocv_download; update md5sum for archives
* fix a bug: macro invoked with incorrect arguments by non-set vars
* enclose if statement
* workable impl
* shorten the var names of two key options
* scalable implementation of downloading from mirror and using custom mirror
* improve ocv_init_download help message
* fix the different extracted directory name in case of ADE & TBB which are downloaded from release page
* improve help message printing
* Download ADE & TBB using commit ids instead of from release pages
* support custom mirrors on downloading archives
* improve hints
* add missing parentheses
* reset ocv_download calls
* mirror support implementation using ocv_cmake_hook & ocv_cmake_hook_append
* move ocv_init_download into cmake/OpenCVDownload.cmake
* move ocv_cmake_hook before checking CMake cache
* improve hints when not fetching as git repo
* add WORKING_DIRECTORY in execute_process in ocv_init_download
* use OPENCV_DOWNLOAD_MIRROR_ID
* add custom.cmake for custom mirror
* detect github origin
* fix broken var name
* download from github by default if custom tbb is set
* add checksum checks for gitcode.cmake before replacing urls and checksums
* add checksum checks for custom.cmake before replacing urls and checkusms
* use description specify instead of set for messages in custom.cmake; use warning message for warnings
* updates and fixes
