Sort exported modpack relationships by identifier

[HebaruSan]

Problem

When you export a modpack into a .ckan file, the mods are in a non-deterministic order. Since the ordering changes from one export to the next, it is difficult to notice changes or track them with code tools like git or diff.

First reported here:

https://forum.kerbalspaceprogram.com/index.php?/topic/205890-%D1%81%D0%BE%D1%80%D1%82%D0%B8%D1%80%D0%BE%D0%B2%D1%89%D0%B8%D0%BA-ckan-%D1%84%D0%B0%D0%B9%D0%BB%D0%B0/

(Found while searching the forum for "CKAN" because I don't have the official CKAN forum thread bookmarked.)

Cause

The order is the order of Registry.Installed(), which is a Dictionary with the identifiers as keys. This is non-deterministic.

Changes

Now we perform a case-insensitive sort by identifier after filtering the sequence and before making the RelationshipDescriptor objects. This should make the ordering consistent.

Documentation for StringComparer.OrdinalIgnoreCase:

https://docs.microsoft.com/en-us/dotnet/api/system.stringcomparer.ordinalignorecase?view=netframework-4.7.2

The StringComparer returned by the OrdinalIgnoreCase property treats the characters in the strings to compare as if they were converted to uppercase using the conventions of the invariant culture, and then performs a simple byte comparison that is independent of language. This is most appropriate when comparing strings that are generated programmatically or when comparing case-insensitive resources such as paths and filenames.