error code for context mismatch on command-queue and events

See discussion: https://github.com/KhronosGroup/OpenCL-Docs/pull/1589#pullrequestreview-4963320073

Many enqueue APIs document `CL_INVALID_CONTEXT` as the error code when the context associated with the passed-in command-queue and events in the event wait list do not match, but some APIs do not, including the two core APIs **clEnqueueUnmapMemObject** and **clEnqueueSVMFree**. Can we require `CL_INVALID_CONTEXT` for these APIs, also? Can we document the same behavior for some of the extension APIs?

Start with the discussion in pull request 1589 and compare the error-code documentation for clEnqueueUnmapMemObject, clEnqueueSVMFree, and the referenced extension APIs. Done means the applicable APIs consistently document CL_INVALID_CONTEXT for mismatched command-queue and event contexts, with the extension scope resolved.

Written by the indexing model from the issue text.