Submission Review Guidelines:

• I have followed the WooCommerce Contributing Guidelines and the WordPress Coding Standards.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• I have reviewed my code for security best practices.
• Following the above guidelines will result in quick merges and clear and detailed feedback when appropriate.

Changes proposed in this Pull Request:

This PR adds a "Copy all content" menu item to the description editor modal.

Known issue:

• The transient notice (snackbar) saying that the copy succeeded is (mostly) hidden under the modal. This will be addressed separately (see Transient notices appear under modals #39208)

Closes #39183.

How to test the changes in this Pull Request:

1. Enable the new block-based product editor.
2. Create a new simple product.
3. Click on "Edit description" to bring up the description modal editor.
4. Enter in a description. Try using some different blocks.
5. Click on the "..." more menu dropdown.
6. Click on the "Copy all content" menu item.
7. Verify that the Tracks event wcadmin_product_iframe_editor_copy_all_content_menu_item_click is logged.
8. Paste in a variety of places and verify the result is correct:
   • Back into description editor... blocks pasted should look identical
   • Into a post editor... blocks pasted should look identical
   • Into a text editor... text should be the standard Gutenberg serialized representation of blocks (HTML with comments)

Changelog entry

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