support profiler_callbacks

[yjh0502]

• add support for IUnityProfilerCallbacks and IUnityProfilerCallbacksV2 with feature flags
• tested on macOS 11.4 & unity 2020.4 LTS

Notes

• Implementation is not optimized for performance (for example using Box<Box<dyn FnMut(...)>>, but it's not terribly slow.
• GetInterface is not working on my environment (not sure why) but GetInterfaceSplit works so I changed to use it.
• updated bindings are generated with unity 2020.4 LTS + Vulkan sdk 1.2.183. I'm not sure if it works on Windows. Should we move bindgen to build.rs for platform portability?
• I assume unity plugin interface to be thread-safe, so I added unsafe impl {Send/Sync} for the interface to make life easier with profiler callback interfaces. As there's no documentation about thread-safety of the interfaces so it might be unsafe :(.

[aosoft]

Thank you for your contribution. I will confirm it.

[aosoft]

I think it is generally OK, but I would like to make some changes.

• The code generated by bindgen has a large difference in the header part, so I re-generated it.
  • I think that using build.rs to run bindgen at compile time can be hard to set up in some cases, and I don't plan to change to that at this time.
• Fixed a build error in d3d12.rs. Unity's PluginAPI seems to have changed.
• I moved the profiler_callbacks::v2 module to profiler_callbacks because I think it is too deep in the hierarchy. d3d12.rs has a similar definition of the extended interface.