This changes the include directive to use the standard C preprocessor
`#include` directive.
The regex to applied to all glsl sources is:
`pragma BLENDER_REQUIRE\((\w+\.glsl)\)`
`include "$1"`
This allow C++ linter to parse the code and allow easier codebase
traversal.
However there is a small catch. While it does work like a standard
include directive when the code is treated as C++, it doesn't when
compiled by our shader backends. In this case, we still use our
dependency concatenation approach instead of file injection.
This means that included files will always be prepended when compiled
to GLSL and a file cannot be appended more than once.
This is why all GLSL lib file should have the `#pragma once` directive
and always be included at the start of the file.
These requirements are actually already enforced by our code-style
in practice.
On the implementation, the source needed to be mutated to comment
the `#pragma once` and `#include`. This is needed to avoid GLSL
compiler error out as this is an extension that not all vendor
supports.
Rel #127983
Pull Request: https://projects.blender.org/blender/blender/pulls/128076
7e5bc58649