Implement batch rename functionality for FileSystemDock

[nongvantinh]

Implement proposal 5633

While FileSystemDock treats its elements as files or folders, SceneTreeDock considers all its elements as Nodes. Additionally, there are differences in what can be included in batch renaming between these two docks. Therefore, I cannot merge the RenameDialog into one.

Current features include:

✅ Batch find and replace.
✅ Rename using Parent folder.
✅ Rename with number counter.
✅ Rename with regex.

[KoBeWi]

The proposal mentions "Batch Rename", because it's the only option of renaming multiple items right now, but wouldn't something like #69087 be better?

[nongvantinh]

No, PR #69087 only performs a partial batch rename for SceneTreeDock. Meanwhile, we already have a batch rename dialog for it (PR #15928), and it offers more functionality than just batch renaming. For instance, you can select all the nodes, but you can also filter the desired nodes using regex and apply custom renaming to the filtered nodes.

While this PR adds the same rename dialog for FileSystemDock (which is different from #69087 and #15928), tailored specifically to work with FileSystemDock.

This PR should not be a problem. However, the only concern here is that we lack the ability to migrate these dialogs to a plugin instead of embedding them in the Godot source code. Whenever I review proposals, I often feel that some features could be implemented as plugins. Unfortunately, we don't have enough flexibility to implement them as plugins, so we have to include them in the Godot source code.