Cleanup: GPU: Update classes comments

This should avoid confusion about what is a class and what is an opaque
pointer.

source/blender/gpu/intern/gpu_batch_private.hh

@@ -32,6 +32,10 @@
 namespace blender {
 namespace gpu {
 
+/**
+ * Base class which is then specialized for each implementation (GL, VK, ...).
+ * NOTE: Extends GPUBatch as we still needs to expose some of the internals to the outside C code.
+ **/
 class Batch : public GPUBatch {
  public:
   Batch(){};

source/blender/gpu/intern/gpu_drawlist_private.hh

@@ -28,6 +28,10 @@
 namespace blender {
 namespace gpu {
 
+/**
+ * Implementation of Multi Draw Indirect.
+ * Base class which is then specialized for each implementation (GL, VK, ...).
+ **/
 class DrawList {
  public:
   virtual ~DrawList(){};

source/blender/gpu/intern/gpu_shader_interface.hh

@@ -45,6 +45,10 @@ typedef struct ShaderInput {
   int32_t binding;
 } ShaderInput;
 
+/**
+ * Implementation of Shader interface.
+ * Base class which is then specialized for each implementation (GL, VK, ...).
+ **/
 class ShaderInterface {
   /* TODO(fclem) should be protected. */
  public:

source/blender/gpu/intern/gpu_shader_private.hh

@@ -29,6 +29,10 @@
 namespace blender {
 namespace gpu {
 
+/**
+ * Implementation of shader compilation and uniforms handling.
+ * Base class which is then specialized for each implementation (GL, VK, ...).
+ **/
 class Shader {
  public:
   /** Uniform & attribute locations for shader. */

source/blender/gpu/intern/gpu_state_private.hh

@@ -151,6 +151,10 @@ inline GPUStateMutable operator~(const GPUStateMutable &a)
   return r;
 }
 
+/**
+ * State manager keeping track of the draw state and applying it before drawing.
+ * Base class which is then specialized for each implementation (GL, VK, ...).
+ **/
 class GPUStateManager {
  public:
   GPUState state;

source/blender/gpu/intern/gpu_uniform_buffer_private.hh

@@ -33,6 +33,10 @@ namespace gpu {
 #  define DEBUG_NAME_LEN 64
 #endif
 
+/**
+ * Implementation of Uniform Buffers.
+ * Base class which is then specialized for each implementation (GL, VK, ...).
+ **/
 class UniformBuf {
  protected:
   /** Data size in bytes. */