fix(editor): loading style (#12537)

Closes: [BS-3555](https://linear.app/affine-design/issue/BS-3555/ui-attachment-loading-变量更新)
Closes: [BS-3559](https://linear.app/affine-design/issue/BS-3559/ui-图片-loading-变量更新)

### Dark
<img width="625" alt="Screenshot 2025-05-26 at 20 32 36" src="https://github.com/user-attachments/assets/93501e3d-8fc6-45f9-84a0-ac147e5c5f9f" />

### Light
<img width="623" alt="Screenshot 2025-05-26 at 20 32 25" src="https://github.com/user-attachments/assets/7d5bc128-6667-45b5-982d-dab3a22706a7" />

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **New Features**
  - Loading icons are now invoked as functions, allowing for more flexible and customizable rendering with parameters like size and progress.

- **Refactor**
  - Replaced theme-dependent and static loading icon references with a unified `LoadingIcon()` component across multiple components and blocks.
  - Removed legacy icon variants and simplified icon import statements, centralizing icon rendering logic.

- **Style**
  - Updated styles for loading and reload buttons to use theme-aware CSS variables.
  - Enlarged and repositioned loading indicators in image blocks for better visibility.

- **Bug Fixes**
  - Achieved consistent loading icon rendering across various blocks and components by standardizing icon invocation.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/gfx/mindmap/src/toolbar/mindmap-importing-placeholder.ts

@@ -1,4 +1,4 @@
-import { LightLoadingIcon } from '@blocksuite/affine-components/icons';
+import { LoadingIcon } from '@blocksuite/affine-components/icons';
 import { unsafeCSSVarV2 } from '@blocksuite/affine-shared/theme';
 import { ShadowlessElement } from '@blocksuite/std';
 import { css, html } from 'lit';
@@ -46,7 +46,7 @@ export class MindMapPlaceholder extends ShadowlessElement {
     return html`<div class="placeholder-container">
       <div class="preview-icon">${importMindMapIcon}</div>
       <div class="description">
-        ${LightLoadingIcon}
+        ${LoadingIcon()}
         <span>Importing mind map...</span>
       </div>
     </div>`;