[UE] Make the reimport menu appear for .atlas and .json and .skel files.

[misaki-eymard]

Description:
In older versions of the Unreal Engine, you could find the Re-import item in the Asset menu no matter which of the files you selected that were needed to make up the skeleton, but in newer versions, Re-import only appears when a .png file is selected. This contradicts the following description currently in the spine-ue runtime documentation:

Note: The Unreal Engine Editor sometimes fails to recognize source file changes. In this case, locate your Spine skeleton data or texture atlas asset in the content browser, double click it, then select Asset -> Re-import from the menu of the newly opened window.

The re-import menu should also appear when right-clicking an asset in the Content Browser, but it does not appear either.

Perhaps newer versions of the Unreal Engine need to specify that the re-import menu should appear for each extension.

Expected behavior:
When you locate your spine skeleton data or texture atlas asset in the Content Browser, double-click it, then select Asset -> Re-import from the menu of the newly opened window.

Steps to reproduce:

1. Open the example project (SpineUE.uproject) with UE 5.5.
2. Navigate to Content/GettingStarted/Assets/Spineboy and double click on the file spineboy.atlas or spineboy-pro.json.
3. Open the Asset menu in the newly opened window. You will see that the menu for reimporting is missing.

To check on the case of .skel files, see Content/GettingStarted/Assets/celestial-circus.

UE versions where this issue has been found:
UE 5.5.3
UE 5.4.4

This issue was reported in the following thread on the forum:
https://esotericsoftware.com/forum/d/28163-spine-unreal-engine-54-reimport-issue