Add ability to sort local Packages group

[mthole]

In my team's project, we primarily use the local SPM packages organized into "layers", with a directional dependency graph. In such a set up, it's super helpful to have the ordering of the layers in the Xcode organizer reflect the logical ordering of the layers. This PR adds that functionality, expanding the groupOrdering configuration to be applied to the local package ordering as well.

[mthole]

This is a bit fragile-- other suggestions welcome!

[jflan-dd]

Another option could be to treat any folder as "group" for the purposes of sorting in setupGroupOrdering with something like this:

    public func setupGroupOrdering(group: PBXGroup) {
        let groupOrdering = project.options.groupOrdering.first { groupOrdering in
            // existing logic ...
        }

        func isGroupOrFolder(_ element: PBXFileElement) -> Bool {
            element is PBXGroup || (element as? PBXFileReference)?.lastKnownFileType == "folder"
        }
        
        if let order = groupOrdering?.order {
            let files = group.children.filter { !isGroupOrFolder($0) }
            var groups = group.children.filter { isGroupOrFolder($0) }
            
            // existing logic ...

[yonaskolb]

Closed in favour of #1466