Add way to query for driver version info without replaying.

* This lets us print what driver is available without opening a capture, useful
  for autotest logging.
* We also print the driver version & vendor on capture as well as replay for all
  APIs. Previously we were only printing this reliably on replay for GL/Vulkan
  but it's useful everywhere for post-mortem debugging.

renderdoc/core/image_viewer.cpp

@@ -170,6 +170,7 @@ public:
     return ret;
   }
   void SavePipelineState() {}
+  DriverInformation GetDriverInfo() { return {GPUVendor::Unknown, ""}; }
   const D3D12Pipe::State *GetD3D12PipelineState() { return NULL; }
   const GLPipe::State *GetGLPipelineState() { return NULL; }
   const VKPipe::State *GetVulkanPipelineState() { return NULL; }