* Adds UAV support for D3D12, Vulkan and reworked support for OpenGL, D3D11
UAV support is now uniform across compute and draw.
To set a UAV you just use bgfx::setImage() and IMAGE2D in the shader, just like in compute.
Due to these changes shaders will have to be recompiled.
The changes include:
- D3D11 requires patching of the UAV slot number (which is now done by modifying the DXBC instead of using a macro)
- If the DXBC binary includes a debug chunk, that is also patched to match the new slot number
- All the other renderers don't need any kind of patching
- There are some shader annotations to better convert the UAV format used in hlsl to spirv
Possibility of further enhancements:
- bgfx::setViewFrameBuffer() only supports binding to a framebuffer or, using BGFX_INVALID_HANDLE, to bind the default backbuffer. This doesn't allow for the case where there is no need to bind to either one of them, for example when using a fragment shader only to read and write to an UAV.
* Bump shader version, because they need to be recompiled.
Currently `const char * str` gets converted to a StringView when its passed to `bx::strFindNl`, incurring a strlen. We have the data to calculate the strlen and fully construct the StringView.
Preferred output coordinate system transformation added.
glTF2.0 is tested with all models from https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0
Static mesh output looks ok for all of them, but as output file format hasn't changed only static mesh is exported. No animation, nodes, materials. etc.
Fixes opaque type in struct error by disabling check.
```
Error: In Vulkan, OpTypeStruct must not contain an opaque type.
%BgfxSampler2D = OpTypeStruct %6 %8
```
Win32/Linux version is from texturev. OSX uses native dialog instead of zenity.
win32 has a fix to support win32 target: OPENFILENAMEA customData is uintptr_t instead of uint64_t.
