Extension Error Codes in cl.h

cl.h currently includes error codes for:

* `CL_INVALID_GL_OBJECT`
* `CL_INVALID_MIP_LEVEL`

These error codes are defined by extensions though, and are not in the core API specification.

Questions are:

* Should they be in cl_ext.h instead?
* Should they have a KHR suffix?

Start by comparing the declarations in cl.h with the extension definitions expected in cl_ext.h and consult the OpenCL API specification for CL_INVALID_GL_OBJECT and CL_INVALID_MIP_LEVEL. Resolve whether these codes belong in the extension header and whether a KHR suffix is required; completion depends on reaching that specification-based decision.

Written by the indexing model from the issue text.