feat: add background fill functionality for layers

- Implemented FillLayerBackgroundCommand to fill the background of layers with a specified color.
- Introduced BackgroundFillManager to manage background fill operations.
- Updated LayerManager to include fillLayerBackground method.
- Enhanced LayersPanel with a color picker for filling layer backgrounds.
- Modified RasterizeLayerCommand to reflect changes in terminology and functionality.
- Adjusted LayerSort to ensure filled layers are rendered at the correct z-index.
- Updated relevant utility functions and components to support new fill feature.

src/component/Canvas/CanvasEditor/managers/BackgroundFillManager.js

@@ -0,0 +1,30 @@
+import { FillLayerBackgroundCommand } from "../commands/FillLayerBackgroundCommand";
+
+export class BackgroundFillManager {
+  constructor({ canvas, layers, commandManager, canvasManager }) {
+    this.canvas = canvas;
+    this.layers = layers;
+    this.commandManager = commandManager;
+    this.canvasManager = canvasManager;
+  }
+
+  /**
+   * 填充指定图层背景
+   * @param {string} layerId 图层ID
+   * @param {string} fillColor 填充颜色
+   */
+  async fillLayerBackground(layerId, fillColor) {
+    const command = new FillLayerBackgroundCommand({
+      canvas: this.canvas,
+      layers: this.layers,
+      layerId,
+      fillColor,
+      canvasManager: this.canvasManager,
+    });
+    if (this.commandManager) {
+      await this.commandManager.execute(command);
+    } else {
+      await command.execute();
+    }
+  }
+}