Improvements to Attachment Hover

The `Attachment Hover` hotkey added in 4.3.22 allows image attachments, such as regions and meshes, to be selected even when a bone is currently selected. However, other attachment types cannot be selected in the same way.

We have received a request to allow other attachment types to be selected as well, so this behavior may be worth reconsidering.

**Possible solutions include:**

- Allow the `Attachment Hover` hotkey to select all attachment types.
- Add a separate hotkey for selecting all attachment types.
- Allow other item types to remain selectable whenever certain viewport options are enabled, without requiring a hotkey. This would restore the behavior available in version 4.2 and earlier.

**Related forum thread:**
https://esotericsoftware.com/forum/d/30456-%E5%8A%A8%E7%94%BB%E6%A8%A1%E5%BC%8F%E4%B8%AD%E4%B8%8D%E8%83%BD%E5%90%8C%E6%97%B6%E9%80%89%E4%B8%AD%E5%A4%9A%E9%A1%B9/5

Start by reviewing the existing Attachment Hover behavior described in this issue and the related forum thread. Determine which attachment types should be selectable and which of the three proposed interaction models is intended; the work is done when the behavior is agreed upon and the affected attachment types can be selected as specified in the viewport.

Written by the indexing model from the issue text.