Rename debug commands, add some new ones

[Rua]

Changelog:

- **Breaking** The debug command buffer commands have been renamed to match Vulkan. They now take a `DebugUtilsLabel` value.
- **Breaking** `end_debug_utils_label` is now `unsafe`, as it requires validation checks that are not implemented yet.
- **Breaking** `DebugCallback` is renamed to `DebugUtilsMessenger` to match Vulkan, and now takes a `DebugUtilsMessengerCreateInfo` to construct. It is now `unsafe` to create, because the the callback cannot call any Vulkan API functions, which Vulkano is unable to check.

- Added debug utils commands to `Queue`.
- Added `Instance::with_debug_utils_messengers`, to provide creation info for messengers that should be used at instance creation and destruction time. This function is also `unsafe`.

Fixes #1872. This PR brings some of the debug stuff up to spec and adds a few missing features. Not everything in this extension is implemented yet, but now at least there's more of it.

[AustinJ235]

Looks good!

[jherico]

The advantage of having a language with namespace support is that you can avoid the naming verbosity of the C structs. I'd argue that MessageSeverity, etc should have remained as the names.

Additionally, it leaves UserCallback as being inconsistent with the rest of the naming scheme, since it should technically be something like DebugUtilsMessengerCallback