Print command stream histogram before crashing

[bejado]

Adds a command stream histogram that is printed immediately before the engine crashes due to a command buffer overflow. To do this without increasing the size of the command stream buffer, we track each command's mExecute pointer and map it to a CommandInfo struct. This enables iterating through the buffer after the fact to tally and log command statistics.

[bejado]

@pixelflinger let me know if you're okay with this approach. I don't love the idea of passing a std::function to flush(), so open to suggestions.