Migrate extensions suites to the new test registration framework

[ahesham-arm]

This covers:

• cl_ext_cxx_for_opencl
• cl_khr_command_buffer
• cl_khr_command_buffer/cl_khr_command_buffer_mutable_dispatch
• cl_khr_dx9_media_sharing
• cl_khr_external_semaphore
• cl_khr_kernel_clock
• cl_khr_semaphore

Contributes to #2181.