Simplify XRT native C++ API usage with less headers to include

[keryell]

It is cumbersome to include many headers for an XRT application.
There should be a single header for most use cases, like xrt/xrt.h or xrt/xrt.hpp or xrt/xrt++.h or [bikesheding].
I think it makes sense today since XRT is becoming less experimental. There could be other includes for very specific/experimental features or extensions.

[bryanloz-xilinx]

I agree here with @keryell. I also think its strange that the existing xrt.h is included by xrt/xrt_device.h it should be the other way around.

[stsoe]

yeah. well, but that xrt.h is completely different from what is being discussed here.

xrt.h is a legacy header file on top of which XRT C++ APIs are built, for example xcl typedefs are in xrt.h and are used in the C++ APIs. This was done early on when the C++ APIs were used in conjunction with xcl APIs. No longer the case, so some cleanup should be done.

Confusing indeed. I will address it as part of this issue.