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_drawlist.cc b/source/blender/gpu/opengl/gl_drawlist.cc
index d8c17084457..0768f7502ce 100644
--- a/source/blender/gpu/opengl/gl_drawlist.cc
+++ b/source/blender/gpu/opengl/gl_drawlist.cc
@@ -76,7 +76,7 @@ GLDrawList::GLDrawList(int length)
   data_ = NULL;
 
   if (USE_MULTI_DRAW_INDIRECT && GLEW_ARB_multi_draw_indirect &&
-      GPU_arb_base_instance_is_supported()) {
+      GLContext::base_instance_support) {
     /* Alloc the biggest possible command list, which is indexed. */
     buffer_size_ = sizeof(GLDrawCommandIndexed) * length;
   }