Ensure equality member consistency for SampleInfo

The previous implementation of `SampleInfo`'s equality members was not
completely correct in its treatment of the `sampleNames` array. While
`Equals()` compared the values of `sampleNames` using `SequenceEqual()`,
therefore performing a structural check that inspects the contents of
both arrays, `GetHashCode()` used `HashCode.Combine()` directly on the
arrays, therefore operating on reference equality. This could cause the
pooling mechanism of samples to fail, as pointed out in #11079.

To resolve, change the `GetHashCode()` implementation such that it also
considers the contents of the array rather than just the reference to
the array itself. This is achieved by leveraging
`StructuralEqualityComparer`.

Additionally, as a bonus, an array sort was added to the constructor of
`SampleInfo`. This is intended to be a "canonicalisation" processing
step for the array of sample names. Thanks to that sort, two instances
of `SampleInfo` that have the same sample names but permutated will also
turn out to be equal and have the same hash codes, given the
implementation of both equality members. This gives `SampleInfo`
set-like semantics.

osu.Game/Audio/SampleInfo.cs

@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 
@@ -17,6 +18,7 @@ namespace osu.Game.Audio
         public SampleInfo(params string[] sampleNames)
         {
             this.sampleNames = sampleNames;
+            Array.Sort(sampleNames);
         }
 
         public IEnumerable<string> LookupNames => sampleNames;
@@ -25,7 +27,9 @@ namespace osu.Game.Audio
 
         public override int GetHashCode()
         {
-            return HashCode.Combine(sampleNames, Volume);
+            return HashCode.Combine(
+                StructuralComparisons.StructuralEqualityComparer.GetHashCode(sampleNames),
+                Volume);
         }
 
         public bool Equals(SampleInfo other)