I am posting a solution for people coming here for an answer to this particular problem of not having c++ classes visible in the editor content browser.
Reproducing this was simple enough by opening some blueprint only project and adding a c++ class. The editor used the c++ classes correctly but they were not visible in the content browser.
The solution to this problem is deleting files and folders that are automatically built or copied the first time a project is opened, forcing unreal editor to recompile and recreate these files. While all below folders and files are not necessary to delete for the fix, it is considered good practice to let unreal editor recreate these files, especially if you are switching from a different engine build.
Delete these files and folders in your project folder:
After you have deleted the files, right-click on .uproject file and click “Generate Visual Studio project files” for Unreal Editor to recompile and recreate the needed files.
Open newly created .sln file with Visual Studio, compile and run the project and you should see your c++ classes in the content browser.