Fix already contains module error at upgrade

[HebaruSan]

Problem

After #3643, upgrades are broken in the dev builds:

1. Install an old version of KSP-Recall
2. Click the upgrade checkbox on that mod's row

System.ArgumentException: Already contains module: KSP-Recall
   at CKAN.RelationshipResolver.Add(CkanModule module, SelectionReason reason)
   at CKAN.RelationshipResolver.AddModulesToInstall(IEnumerable`1 modules)
   at CKAN.RelationshipResolver..ctor(IEnumerable`1 modulesToInstall, IEnumerable`1 modulesToRemove, RelationshipResolverOptions options, IRegistryQuerier registry, GameVersionCriteria GameVersion)
   at CKAN.IRegistryQuerierHelpers.FindRemovableAutoInstalled(IRegistryQuerier querier, List`1 installedModules, HashSet`1 dlls, IDictionary`2 dlc, GameVersionCriteria crit)
   at CKAN.IRegistryQuerierHelpers.FindRemovableAutoInstalled(IRegistryQuerier querier, List`1 installedModules, GameVersionCriteria crit)
   at CKAN.GUI.ModList.ComputeChangeSetFromModList(IRegistryQuerier registry, HashSet`1 changeSet, ModuleInstaller installer, GameVersionCriteria version)
   at CKAN.GUI.ManageMods.<UpdateChangeSetAndConflicts>d__117.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at CKAN.GUI.ManageMods.<ModList_CellValueChanged>d__74.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()

Reported on Discord by @TwiceDaIce, who was not able to submit an issue at the time.

Cause

The exception indicates that the list of modules passed to the resolver contained a duplicate. This was supposed to be prevented by the way FindRemovableAutoInstalled's parameter is constructed, but modules_to_remove doesn't contain the installed version (as I assumed it would by its name since that version would be removed). This duplicate would always have been there for upgrades, but prior to #3643 it didn't matter because we weren't passing the modules to a resolver.

Tried and failed

I tried adding the installed module to modules_to_remove, and this broke switching from one module version to another. There are too many uses of these variables and too many implicit assumptions about how they behave for me to sort it out that way.

Changes

Now a new InstalledAfterChanges function generates exactly the list of modules that I want, without duplicates, so upgrading and switching versions both work.

[techman83]

That looks sensible, thanks @HebaruSan !