Remove DNA headers, using forward declarations where possible.
Also removed duplicate header, header including it's self
and unnecessary inclusion of libc system headers from BKE header.
This replaces header include guards with `#pragma once`.
A couple of include guards are not removed yet (e.g. `__RNA_TYPES_H__`),
because they are used in other places.
This patch has been generated by P1561 followed by `make format`.
Differential Revision: https://developer.blender.org/D8466
This patch will make use of the eDrawType where it was used as a
variable or parameter name. The eObjectDrawType was renamed to eDrawType
as it is also used by `View3DShading.type`.
Motivation the functions get 3 different kind of flag parameters (ImBuf,
DrawType, OffscreenRendering) the naming of the flags were not clear,
leading to mistakes and unnecessary time spend debugging.
