feat: add basic pasters (#7331)

* feat: implement basic IPaster interface

* feat: add pasters for blocks and workspace comments

core/clipboard/block_paster.ts

@@ -0,0 +1,31 @@
+/**
+ * @license
+ * Copyright 2023 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import {BlockSvg} from '../block_svg.js';
+import {CopyData} from '../interfaces/i_copyable';
+import {IPaster} from '../interfaces/i_paster.js';
+import {State, append} from '../serialization/blocks';
+import {Coordinate} from '../utils/coordinate.js';
+import {WorkspaceSvg} from '../workspace_svg.js';
+
+export class BlockPaster implements IPaster<BlockCopyData, BlockSvg> {
+  paste(
+    copyData: BlockCopyData,
+    workspace: WorkspaceSvg,
+    coordinate?: Coordinate,
+  ): BlockSvg | null {
+    if (!workspace.isCapacityAvailable(copyData.typeCounts!)) return null;
+
+    const state = copyData.saveInfo as State;
+    if (coordinate) {
+      state['x'] = coordinate.x;
+      state['y'] = coordinate.y;
+    }
+    return append(state, workspace, {recordUndo: true}) as BlockSvg;
+  }
+}
+
+export interface BlockCopyData extends CopyData {}