Clarifying spec behavior for CL_DEVICE_TYPE_ALL

Would like to confirm that this interpretation of the spec is accurate.

For a platform with multiple devices including a device of type CL_DEVICE_TYPE_CUSTOM, the only API expected to work are:
- clGetDeviceIDs when invoked with CL_DEVICE_TYPE_ALL will return all devices including the custom device
- clCreateContextFromType when invoked with CL_DEVICE_TYPE_ALL will create a context that includes all of these devices
- For a context thus created, clGetContextInfo will work as defined in the spec, including returning all included devices when param_name is CL_CONTEXT_DEVICES

Calling any other API on a multi-device context that includes a custom device will result in undefined/implementation defined behavior.

Review the OpenCL specification sections for clGetDeviceIDs, clCreateContextFromType, and clGetContextInfo, focusing on CL_DEVICE_TYPE_ALL and contexts containing CL_DEVICE_TYPE_CUSTOM. The work is complete when the specification explicitly confirms or corrects the interpretation described in the issue.

Written by the indexing model from the issue text.