GPUExtensions: GL backend isolation

This is part of the Vulkan task T68990.

This commits changes a few things:
- Rename extensions to capabilities (but left the file name untouched).
- Cubemap mip render workaround detection is rewritten using gl
  commands to avoid using the GPU API before initialization.
- Put all the capabilities that are only relevant for the GL backend
  inside GLContext as static variables.
- Cleanup the names of the limit variables.
- Separate all GL related workaround search inside the GL module.

1 files changed, 1 insertions, 1 deletions

diff --git a/source/blender/gpu/opengl/gl_framebuffer.cc b/source/blender/gpu/opengl/gl_framebuffer.cc
index 4be471b236a..506a945d9d4 100644
--- a/source/blender/gpu/opengl/gl_framebuffer.cc
+++ b/source/blender/gpu/opengl/gl_framebuffer.cc
@@ -208,7 +208,7 @@ void GLFrameBuffer::update_attachments(void)
     }
   }
 
-  if (GPU_unused_fb_slot_workaround()) {
+  if (GLContext::unused_fb_slot_workaround) {
     /* Fill normally un-occupied slots to avoid rendering artifacts on some hardware. */
     GLuint gl_tex = 0;
     /* NOTE: Inverse iteration to get the first color texture. */