Fix updateMutableCommands template to use std::array::size() and const pointers

[banan328]

This pull request fixes this commit #298:

• Replaced configs.length() with configs.size() to correctly retrieve the array size.
• Changed configs to std::array<const void*, ArrayLength> for better const-correctness.
• Passed config_types.data(), configs.data() directly to pfn_clUpdateMutableCommandsKHR.

[bashbaug]

Could you add a test for this function?

(It would have been good to do that previously, since it probably would have caught these bugs earlier.)

[EwanC]

Could you add a test for this function?

(It would have been good to do that previously, since it probably would have caught these bugs earlier.)

There is an open PR #276 with some testing, will probably be a bit stale and need updated but could prioritize getting that in as a follow-up.