vulkan: refactor DebugReportCallbackList

Simplify DebugReportCallbackList to be a thread-safe list with three
methods:

 - AddCallback adds a node to the list
 - RemoveCallback removes a node from the list
 - Message invokes each of the nodes on the list

Add some static methods for Node* and VkDebugReportCallbackEXT
conversions.

Bug: 28120066
Change-Id: I109c6eff368cacb37508e2549dbd0b5dfa23bcb3