Add fuzzing infra

fuzz/Emby.Server.Implementations.Fuzz/Emby.Server.Implementations.Fuzz.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net5.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Reference Include="Emby.Server.Implementations">
+      <HintPath>Emby.Server.Implementations.dll</HintPath>
+    </Reference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="SharpFuzz" Version="1.6.2" />
+  </ItemGroup>
+
+</Project>

fuzz/Emby.Server.Implementations.Fuzz/Program.cs

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+using System;
+using Emby.Server.Implementations.Library;
+using SharpFuzz;
+
+namespace Emby.Server.Implementations.Fuzz
+{
+    public static class Program
+    {
+        public static void Main(string[] args)
+        {
+            switch (args[0])
+            {
+                case "PathExtensions.TryReplaceSubPath": Run(PathExtensions_TryReplaceSubPath); return;
+                default: throw new ArgumentException($"Unknown fuzzing function: {args[0]}");
+            }
+        }
+
+        private static void Run(Action<string> action) => Fuzzer.OutOfProcess.Run(action);
+
+        private static void PathExtensions_TryReplaceSubPath(string data)
+        {
+            // Stupid, but it worked
+            var parts = data.Split(':');
+            if (parts.Length != 3)
+            {
+                return;
+            }
+
+            _ = PathExtensions.TryReplaceSubPath(parts[0], parts[1], parts[2], out _);
+        }
+    }
+}

fuzz/Emby.Server.Implementations.Fuzz/Testcases/PathExtensions.TryReplaceSubPath/test1.txt

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+/fuzz/Emby.Server.Implementations.Fuzz/Testcases/PathExtensions.TryReplaceSubPath/test1.txt/:/home/bond/dev/jellyfin/:/srv/jellyfin/

fuzz/Emby.Server.Implementations.Fuzz/fuzz.sh

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+#!/bin/sh
+
+set -e
+
+dotnet build -c Release ../../Emby.Server.Implementations/Emby.Server.Implementations.csproj --output bin
+sharpfuzz bin/Emby.Server.Implementations.dll
+cp bin/Emby.Server.Implementations.dll .
+
+dotnet build
+mkdir -p Findings
+AFL_SKIP_BIN_CHECK=1 afl-fuzz -i "Testcases/$1" -o "Findings/$1" -t 5000 -m 10240 dotnet bin/Debug/net5.0/Emby.Server.Implementations.Fuzz.dll "$1"