Migrate away from MEF for loading DLLs in Windows PowerShell

PSScriptAnalyzer's .NET Framework builds depend on a lesser known technology called the Managed Extensibility Framework (namespaced to System.ComponentModel.Composition) to do a kind of lazy loading of assemblies for rules, presumably for custom rule sets.

This seems to be a kind of inversion of control framework, although we use it in a less typical way than a web server might:

https://github.com/PowerShell/PSScriptAnalyzer/blob/cfeb7d5f510763ba33a9a4ec73259d7d6ea86fdb/Engine/ScriptAnalyzer.cs#L930-L969

It also means that for rules to be discoverable they need to be decorated with attributes like here:
https://github.com/PowerShell/PSScriptAnalyzer/blob/cfeb7d5f510763ba33a9a4ec73259d7d6ea86fdb/Rules/AvoidGlobalFunctions.cs#L18-L20

All of that is fine, and it may be that PSScriptAnalyzer users are having success with it, but I'm not really sure if anyone is using it.

There are two problems:

• We aren't using (and don't seem to need) MEF in PowerShell Core (it apparently has been ported, but it's not clear to what extent).
• MEF loads assemblies differently to PowerShell

This problem raised itself in https://github.com/PowerShell/PSScriptAnalyzer/pull/1133, where a rule that depended on an external assembly, which in turn depended on a third assembly failed to load only in .NET Framework (and behaved differently across PowerShell versions).

The error looked like this:

System.Reflection.ReflectionTypeLoadException: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.
   at System.Reflection.RuntimeModule.GetTypes(RuntimeModule module)
   at System.Reflection.Assembly.GetTypes()
   at System.ComponentModel.Composition.Hosting.AssemblyCatalog.get_InnerCatalog()
   at System.ComponentModel.Composition.Hosting.AssemblyCatalog.GetEnumerator()
   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Microsoft.Windows.PowerShell.ScriptAnalyzer.SafeDirectoryCatalog..ctor(String folderLocation, IOutputWriter outputWriter)
System.ComponentModel.Composition.CompositionException: The composition produced a single composition error. The root cause is provided below. Review the CompositionException.Errors property for more detailed information.
1) Could not load file or assembly 'Newtonsoft.Json, Version=10.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
Resulting in: An exception occurred while trying to create an instance of type 'Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules.UseCompatibleCommands'.
Resulting in: Cannot activate part 'Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules.UseCompatibleCommands'.
Element: Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules.UseCompatibleCommands -->  Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules.UseCompatibleCommands -->  AssemblyCatalog (Assembly="Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules, Version=1.17.1.0, Culture=neutral, PublicKeyToken=null")
Resulting in: Cannot get export 'Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules.UseCompatibleCommands (ContractName="Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic.IScriptRule")' from part 'Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules.UseCompatibleCommands'.
Element: Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules.UseCompatibleCommands (ContractName="Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic.IScriptRule") -->  Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules.UseCompatibleCommands -->  AssemblyCatalog (Assembly="Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules, Version=1.17.1.0, Culture=neutral, PublicKeyToken=null")
Resulting in: Cannot set import 'Microsoft.Windows.PowerShell.ScriptAnalyzer.ScriptAnalyzer.ScriptRules (ContractName="Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic.IScriptRule")' on part 'Microsoft.Windows.PowerShell.ScriptAnalyzer.ScriptAnalyzer'.
Element: Microsoft.Windows.PowerShell.ScriptAnalyzer.ScriptAnalyzer.ScriptRules (ContractName="Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic.IScriptRule") -->  Microsoft.Windows.PowerShell.ScriptAnalyzer.ScriptAnalyzer
   at System.ComponentModel.Composition.CompositionResult.ThrowOnErrors(AtomicComposition atomicComposition)
   at System.ComponentModel.Composition.Hosting.ComposablePartExportProvider.Compose(CompositionBatch batch)
   at Microsoft.Windows.PowerShell.ScriptAnalyzer.ScriptAnalyzer.LoadRules(Dictionary`2 result, CommandInvocationIntrinsics invokeCommand, Boolean loadBuiltInRules)

At some point, the compatibility rule would depend on Microsoft.PowerShell.CrossCompatibility.dll, which in turn depended on Newtonsoft.Json.dll.

The first load would succeed, but the second would fail because it would only look for Newtonsoft.Json.dll in the directory of powershell.exe rather than in the same directory as Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules.dll.

This was resolved by adding Add-Type $newtonsoftDllPath to ScriptAnalyzer.psm1.

This may not actually be due to MEF, but is worth investigating in any case. The DLL loading differences between Windows PS and PS Core are here:

https://github.com/PowerShell/PSScriptAnalyzer/blob/cfeb7d5f510763ba33a9a4ec73259d7d6ea86fdb/Engine/ScriptAnalyzer.cs#L930-L969

先查看 Engine/ScriptAnalyzer.cs 中 930-969 行附近的 DLL 加载路径，然后阅读 ScriptAnalyzer.psm1 以及 Rules/AvoidGlobalFunctions.cs 中的规则元数据。将 issue 中描述的 Windows PowerShell 和 PowerShell Core 行为与 pull request 1133 中的失败进行比较；完成的标准是提供有文档记录且经过测试的替代方案，或明确决定是否应移除 MEF。