When opening a lot of scenes at the same time it can take a lot of time during which the editor will be unresponsive.

### Tested versions

4.3.dev[578d937927ea9735aa7a8e0535f57801406b0b82]

### System information

macOS 13.3.0 - Vulkan (Forward+) - integrated Apple M1 Pro - Apple M1 Pro (8 Threads)

### Issue description

This is similar to #89516. Here it happens when you try to open a lot of scenes at the same time. there is no way to make it go faster so just adding a progress bar would fix it. Same thing happens on closing scenes.

### Steps to reproduce

1. open the MRP
2. select all scenes
3. right click and press "Open Scenes"
4. see the editor being unresponsive
5. right click on one of the scene and select "Close All Tabs"
6. See the editor being unresponsive again

### Minimal reproduction project (MRP)

[LongGroups.zip](https://github.com/godotengine/godot/files/14616584/LongGroups.zip)
this is the mrp from #89516

Start with the LongGroups.zip minimal reproduction and follow the reported Open Scenes and Close All Tabs steps in the Godot editor. Inspect the editor paths handling scene opening and closing, then verify that both operations show progress instead of leaving the editor unresponsive.

Written by the indexing model from the issue text.