Unit tests: replace mock and compat with code from community.internal_test_tools (#9921)
* Replace compat with equivalent from community.internal_test_tools.
* Replace mock with equivalent from community.internal_test_tools.
(cherry picked from commit 410cf72aec)
Co-authored-by: Felix Fontein <felix@fontein.de>
* Move licenses to LICENSES/, run add-license.py, add LICENSES/MIT.txt.
* Replace 'Copyright:' with 'Copyright'
sed -i 's|Copyright:\(.*\)|Copyright\1|' $(rg -l 'Copyright:')
Co-authored-by: Maxwell G <gotmax@e.email>