Capture OpenCL version required by individual extensions

[kpet]

Prior to the unification of the OpenCL specifications, the specification for many extensions stated the version of OpenCL required by the extension. The new extension appendix no longer seems to have the information. We should capture dependency information in the XML (OpenCL version and other extensions) and add that to the generated information in the extension appendix. Relates to #1165

[kpet]

Observed in the 2024/05/14 teleconference: we do have some of the information in the XML already and we are using it in header generation:

        <extension name="cl_khr_command_buffer" revision="0.9.4" supported="opencl" depends="CL_VERSION_1_2" ratified="opencl" provisional="true">

[bashbaug]

Somewhat related to #993.

Possible resolution, as discussed in the June 4th teleconference:

• Add the required OpenCL version in the XML file, as a required field.
• Include this information in the generated asciidoc snippets for each extension.