buffer_cache: Return handles instead of pointer to handles

The original idea of returning pointers is that handles can be moved.
The problem is that the implementation didn't take that in mind and made
everything harder to work with. This commit drops pointer to handles and
returns the handles themselves. While it is still true that handles can
be invalidated, this way we get an old handle instead of a dangling
pointer.

This problem can be solved in the future with sparse buffers.

src/video_core/renderer_opengl/utils.h

@@ -11,49 +11,6 @@
 
 namespace OpenGL {
 
-class StateTracker;
-
-class VertexArrayPushBuffer final {
-public:
-    explicit VertexArrayPushBuffer(StateTracker& state_tracker);
-    ~VertexArrayPushBuffer();
-
-    void Setup();
-
-    void SetIndexBuffer(const GLuint* buffer);
-
-    void SetVertexBuffer(GLuint binding_index, const GLuint* buffer, GLintptr offset,
-                         GLsizei stride);
-
-    void Bind();
-
-private:
-    struct Entry;
-
-    StateTracker& state_tracker;
-
-    const GLuint* index_buffer{};
-    std::vector<Entry> vertex_buffers;
-};
-
-class BindBuffersRangePushBuffer final {
-public:
-    explicit BindBuffersRangePushBuffer(GLenum target);
-    ~BindBuffersRangePushBuffer();
-
-    void Setup();
-
-    void Push(GLuint binding, const GLuint* buffer, GLintptr offset, GLsizeiptr size);
-
-    void Bind();
-
-private:
-    struct Entry;
-
-    GLenum target;
-    std::vector<Entry> entries;
-};
-
 void LabelGLObject(GLenum identifier, GLuint handle, VAddr addr, std::string_view extra_info = {});
 
 } // namespace OpenGL