Fix exception when the same module is in multiple repos

[HebaruSan]

Problem

KSP-CKAN/NetKAN#10303 is throwing:

Unhandled Exception:
  System.ArgumentException: An item with the same key has already been added. Key: RSSOrigin-TopoRevampTextures16k v1.1.2
    at System.Collections.Generic.Dictionary`2[TKey,TValue].TryInsert (TKey key, TValue value, System.Collections.Generic.InsertionBehavior behavior) [0x0015a] in <d636f104d58046fd9b195699bcb1a744>:0 
    at System.Collections.Generic.Dictionary`2[TKey,TValue].Add (TKey key, TValue value) [0x00000] in <d636f104d58046fd9b195699bcb1a744>:0 
    at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement] (System.Collections.Generic.List`1[T] source, System.Func`2[T,TResult] keySelector, System.Func`2[T,TResult] elementSelector, System.Collections.Generic.IEqualityComparer`1[T] comparer) [0x0002d] in <69ada62907b24213a012734531df1db1>:0 
    at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement] (System.Collections.Generic.IEnumerable`1[T] source, System.Func`2[T,TResult] keySelector, System.Func`2[T,TResult] elementSelector, System.Collections.Generic.IEqualityComparer`1[T] comparer) [0x00067] in <69ada62907b24213a012734531df1db1>:0 
    at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement] (System.Collections.Generic.IEnumerable`1[T] source, System.Func`2[T,TResult] keySelector, System.Func`2[T,TResult] elementSelector) [0x00000] in <69ada62907b24213a012734531df1db1>:0 
    at CKAN.ResolvedByNew..ctor (CKAN.CkanModule source, CKAN.RelationshipDescriptor relationship, CKAN.SelectionReason reason, System.Collections.Generic.IEnumerable`1[T] providers, System.Collections.Generic.ICollection`1[T] definitelyInstalling, System.Collections.Generic.ICollection`1[T] allInstalling, CKAN.IRegistryQuerier registry, System.Collections.Generic.ICollection`1[T] dlls, System.Collections.Generic.ICollection`1[T] installed, CKAN.Versioning.GameVersionCriteria crit, CKAN.OptionalRelationships optRels, System.Collections.Concurrent.ConcurrentDictionary`2[TKey,TValue] relationshipCache) [0x0004d] in <dc3376c212ad46a191d66621f410eae2>:0 

Cause

This exception indicates that Registry.LatestAvailableWithProvides returned multiple copies of RSSOrigin-TopoRevampTextures16k, which would have happened because it's present in both the default repo and the custom repo that the validator uses for the freshly inflated replacement modules. It should only return the one with the higher repo priority.

Changes

• Now the value type of the provides index is changed from HashSet to array to preserve the priority ordering of the source repos
• Now Registry.LatestAvailableWithProvides calls Distinct to filter duplicates out of its returned list