docs: update v0 languages for device layer deprecation

Clarify that a layer's

  vkEnumerateInstanceLayerProperties
  vkEnumerateInstanceExtensionProperties
   - should enumerate the layer itself

  vkEnumerateDeviceLayerProperties
   - is deprecated

  vkEnumerateDeviceExtensionProperties
   - must handle all layers by chaining

  vkCreateInstance
   - `pNext` handling is covered by the spec

  vkCreateDevice
   - allow validation layers to validate layer and extension names

Clarify that the layer library's

  vkEnumerateInstanceLayerProperties
  vkEnumerateInstanceExtensionProperties
   - are not used by the desktop loader
   - can be aliases to the layer's versions when the layer library
     contains only one layer

  vkEnumerateDeviceLayerProperties
  vkEnumerateDeviceExtensionProperties
   - are not used by the desktop loader

  vkGetInstanceProcAddr
   - mention that the special cases for vkCreateDevice and device commands
     are for compatibility
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