Refactor: Make header files more clangd and clang-tidy friendly

When using clangd or running clang-tidy on headers there are
currently many errors. These are noisy in IDEs, make auto fixes
impossible, and break features like code completion, refactoring
and navigation.

This makes source/blender headers work by themselves, which is
generally the goal anyway. But #includes and forward declarations
were often incomplete.

* Add #includes and forward declarations
* Add IWYU pragma: export in a few places
* Remove some unused #includes (but there are many more)
* Tweak ShaderCreateInfo macros to work better with clangd

Some types of headers still have errors, these could be fixed or
worked around with more investigation. Mostly preprocessor
template headers like NOD_static_types.h.

Note that that disabling WITH_UNITY_BUILD is required for clangd to
work properly, otherwise compile_commands.json does not contain
the information for the relevant source files.

For more details see the developer docs:
https://developer.blender.org/docs/handbook/tooling/clangd/

Pull Request: https://projects.blender.org/blender/blender/pulls/132608

intern/eigen/eigen_capi.h

@@ -9,9 +9,9 @@
 #ifndef __EIGEN_C_API_H__
 #define __EIGEN_C_API_H__
 
-#include "intern/eigenvalues.h"
-#include "intern/linear_solver.h"
-#include "intern/matrix.h"
-#include "intern/svd.h"
+#include "intern/eigenvalues.h"    // IWYU pragma: export
+#include "intern/linear_solver.h"  // IWYU pragma: export
+#include "intern/matrix.h"         // IWYU pragma: export
+#include "intern/svd.h"            // IWYU pragma: export
 
 #endif /* __EIGEN_C_API_H__ */