[control group] do not render control group when there are no controls (#190521)

PR updates ControlGroup to not render any components when there are no
controls. PR also removes loading state from ControlGroup, as suggested
by @ThomThomson

#### Before
<img width="600" alt="Screenshot 2024-08-14 at 9 18 57 AM"
src="https://github.com/user-attachments/assets/e52aabf5-7322-4d8e-838c-d56524ece55e">


### Test instructions
1. start kibana with `yarn start --run-examples`
2. Open controls example at http://localhost:5601/app/controlsExamples
3. Remove all controls. Notice how the ControlGroup no longer takes up
any empty vertical spacing
<img width="600" alt="Screenshot 2024-08-14 at 9 15 53 AM"
src="https://github.com/user-attachments/assets/374ddec4-30c5-46fb-8ed9-c8c41a35fc1e">

examples/controls_example/public/app/react_control_example/react_control_example.tsx

@@ -219,6 +219,19 @@ export const ReactControlExample = ({
     };
   }, [controlGroupApi, timeslice$]);
 
+  const [hasControls, setHasControls] = useState(false);
+  useEffect(() => {
+    if (!controlGroupApi) {
+      return;
+    }
+    const subscription = controlGroupApi.children$.subscribe((children) => {
+      setHasControls(Object.keys(children).length > 0);
+    });
+    return () => {
+      subscription.unsubscribe();
+    };
+  }, [controlGroupApi]);
+
   useEffect(() => {
     const subscription = combineLatest([controlGroupFilters$, unifiedSearchFilters$]).subscribe(
       ([controlGroupFilters, unifiedSearchFilters]) => {
@@ -389,7 +402,7 @@ export const ReactControlExample = ({
           reload$.next();
         }}
       />
-      <EuiSpacer size="m" />
+      {hasControls && <EuiSpacer size="m" />}
       <ReactEmbeddableRenderer
         onApiAvailable={(api) => {
           dashboardApi?.setChild(api);
@@ -402,6 +415,7 @@ export const ReactControlExample = ({
           getSerializedStateForChild: getControlGroupSerializedState,
           getRuntimeStateForChild: getControlGroupRuntimeState,
         })}
+        panelProps={{ hideLoader: true }}
         key={`control_group`}
       />
       <EuiSpacer size="l" />

src/plugins/controls/public/react_controls/control_group/components/control_group.tsx

@@ -7,6 +7,7 @@
  */
 
 import React, { useCallback, useEffect, useMemo, useState } from 'react';
+import { css } from '@emotion/react';
 import { BehaviorSubject } from 'rxjs';
 import {
   DndContext,
@@ -24,14 +25,7 @@ import {
   SortableContext,
   sortableKeyboardCoordinates,
 } from '@dnd-kit/sortable';
-import {
-  EuiButtonIcon,
-  EuiFlexGroup,
-  EuiFlexItem,
-  EuiLoadingChart,
-  EuiPanel,
-  EuiToolTip,
-} from '@elastic/eui';
+import { EuiButtonIcon, EuiFlexGroup, EuiFlexItem, EuiPanel, EuiToolTip } from '@elastic/eui';
 import { useBatchedPublishingSubjects } from '@kbn/presentation-publishing';
 import { ControlStyle } from '../../..';
 import { ControlsInOrder } from '../init_controls_manager';
@@ -114,8 +108,15 @@ export function ControlGroup({
     );
   }, [hasUnappliedSelections, applySelections]);
 
+  if (controlsInOrder.length === 0) {
+    return null;
+  }
+
   return (
     <EuiPanel
+      css={css`
+        display: ${isInitialized ? 'none' : 'default'};
+      `}
       borderRadius="m"
       paddingSize="none"
       color={draggingId ? 'success' : 'transparent'}
@@ -127,7 +128,6 @@ export function ControlGroup({
         responsive={false}
         data-test-subj="controls-group"
       >
-        {!isInitialized && <EuiLoadingChart />}
         <EuiFlexItem>
           <DndContext
             onDragStart={({ active }) => setDraggingId(`${active.id}`)}
@@ -167,7 +167,7 @@ export function ControlGroup({
             </DragOverlay>
           </DndContext>
         </EuiFlexItem>
-        {isInitialized && !autoApplySelections && (
+        {!autoApplySelections && (
           <EuiFlexItem grow={false} className="controlGroup--endButtonGroup">
             {hasUnappliedSelections ? (
               ApplyButtonComponent

src/plugins/embeddable/public/react_embeddable_system/react_embeddable_renderer.tsx

@@ -65,6 +65,7 @@ export const ReactEmbeddableRenderer = <
     | 'showBorder'
     | 'showBadges'
     | 'showNotifications'
+    | 'hideLoader'
     | 'hideHeader'
     | 'hideInspector'
   >;

src/plugins/presentation_panel/public/panel_component/presentation_panel.tsx

@@ -50,7 +50,7 @@ export const PresentationPanel = <
   }, []);
 
   if (loading)
-    return (
+    return props.hideLoader ? null : (
       <PanelLoader
         showShadow={props.showShadow}
         showBorder={props.showBorder}

src/plugins/presentation_panel/public/panel_component/types.ts

@@ -40,6 +40,10 @@ export interface PresentationPanelInternalProps<
   showBadges?: boolean;
   showNotifications?: boolean;
 
+  /**
+   * Set to true to not show PanelLoader component while Panel is loading
+   */
+  hideLoader?: boolean;
   hideHeader?: boolean;
   hideInspector?: boolean;