Improve the clipping attachment workflow

The following two improvements have been suggested for the clipping attachment workflow:

**1. Allow choosing the insertion point and end slot when creating a clipping attachment**

Currently, when creating a clipping attachment, the workflow only allows the user to specify the attachment name and define the clipping polygon. It is not possible to choose where the clipping attachment's slot will be inserted in the draw order or specify the end slot during creation. The clipping attachment's slot is always created at the bottom of the draw order.

However, if the clipping attachment needs to be placed somewhere other than the bottom, adjusting its draw order and assigning the end slot afterward can become cumbersome, especially in large projects with many slots. Finding the correct slot and moving it to the desired position may require considerable manual work.

It would be more convenient if users could specify which slot the clipping should begin from during the initial creation process. This would allow the clipping attachment to be inserted at the desired draw order position and make the overall workflow significantly more efficient.

**2. Do not cancel "Choose End Slot" mode when using tree view filters or search**

Currently, after entering "Choose End Slot" mode by clicking the pencil button next to the `End Slot` field, interacting with the tree view filter buttons immediately cancels Choose End Slot mode.

The same thing happens when using the Text search field. Pressing Enter after typing a search term or navigating the search results with the arrow buttons also exits Choose End Slot mode.

For complex skeletons, users may want to filter the tree view or search for a slot by name while they are choosing the end slot. It would therefore be helpful if these operations did not interrupt Choose End Slot mode, allowing users to continue selecting the end slot after filtering or searching.

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**Related forum thread:**

https://esotericsoftware.com/forum/d/30381-%E8%AF%B7%E6%B1%82%E6%BB%91%E5%9D%97%E7%BA%A6%E6%9D%9F%E7%9A%84%E5%8E%9F%E5%8A%A8%E7%94%BB%E5%B8%8C%E6%9C%9B%E8%83%BD%E8%B0%83%E6%95%B4%E5%85%B3%E9%94%AE%E5%B8%A7%E6%95%B0%E5%80%BC/7

Start by reproducing clipping attachment creation and the Choose End Slot workflow in the Spine editor. Verify that creation can select the insertion and end slots, and that tree filters and text search leave Choose End Slot mode active so selection can continue.

Written by the indexing model from the issue text.