move vao from WorkspaceSceneOpenGL to GlxContext

EglContext already had a vao, and it makes more sense for the context to
take care of this than the scene

src/backends/x11/standalone/glxcontext.cpp

@@ -21,10 +21,20 @@ GlxContext::GlxContext(::Display *display, GLXWindow window, GLXContext handle)
     , m_window(window)
     , m_handle(handle)
 {
+    // It is not legal to not have a vertex array object bound in a core context
+    // to make code handling old and new OpenGL versions easier, bind a dummy vao that's used for everything
+    if (!isOpenglES() && hasOpenglExtension(QByteArrayLiteral("GL_ARB_vertex_array_object"))) {
+        glGenVertexArrays(1, &m_vao);
+        glBindVertexArray(m_vao);
+    }
 }
 
 GlxContext::~GlxContext()
 {
+    if (m_vao) {
+        makeCurrent();
+        glDeleteVertexArrays(1, &m_vao);
+    }
     glXDestroyContext(m_display, m_handle);
 }
 

src/backends/x11/standalone/glxcontext.h

@@ -30,6 +30,7 @@ private:
     ::Display *const m_display;
     const GLXWindow m_window;
     const GLXContext m_handle;
+    uint32_t m_vao = 0;
 };
 
 }

src/scene/workspacescene_opengl.cpp

@@ -43,11 +43,6 @@ WorkspaceSceneOpenGL::WorkspaceSceneOpenGL(OpenGLBackend *backend)
     : WorkspaceScene(std::make_unique<ItemRendererOpenGL>())
     , m_backend(backend)
 {
-    // It is not legal to not have a vertex array object bound in a core context
-    if (!GLPlatform::instance()->isGLES() && hasGLExtension(QByteArrayLiteral("GL_ARB_vertex_array_object"))) {
-        glGenVertexArrays(1, &vao);
-        glBindVertexArray(vao);
-    }
 }
 
 WorkspaceSceneOpenGL::~WorkspaceSceneOpenGL()