Improve clUpdateMutableCommandsKHR error wording

As [raised in a PR review](https://github.com/KhronosGroup/OpenCL-Docs/pull/1045#discussion_r1672096624) the error wording around `clUpdateMutableCommandsKHR()` could be improved.

There are many errors that can be returned here based on errors returned by core OpenCL entry-points, as well as invalid usage of the entry-point itself. This makes the current language quite dense, we should improve the readability.

One idea is to categories errors in the description of commands such that we could refer to the categories later on.

Start with the clUpdateMutableCommandsKHR() description and the linked PR review discussion. Identify the error categories needed to make the current dense wording readable, then revise the description so those categories can be referred to consistently; done means the full set of core-entry-point and invalid-usage errors is clearer.

Written by the indexing model from the issue text.