Uninstalled add-ins aren't properly removed #1192
Description
After an add-in is uninstalled, e.g. the Night Vision add-in, on the next launch the add-in is still registered even though some files are missing:
Pinta: Failed to initialize add-in
System.IO.FileNotFoundException: Could not load file or assembly 'NightVisionAddin, Version=1.3.1.0, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.
File name: 'NightVisionAddin, Version=1.3.1.0, Culture=neutral, PublicKeyToken=null'
---> System.IO.FileNotFoundException: Could not load file or assembly '/Users/cameron/Library/Application Support/Pinta/addins/addins/NightVisionEffect.1.3.2/NightVisionAddin.dll'. The system cannot find the file specified.
File name: '/Users/cameron/Library/Application Support/Pinta/addins/addins/NightVisionEffect.1.3.2/NightVisionAddin.dll'
at System.Runtime.Loader.AssemblyLoadContext.LoadFromAssemblyPath(String assemblyPath)
at System.Reflection.Assembly.LoadFrom(String assemblyFile)
at Mono.Addins.AddinEngine.CurrentDomainAssemblyResolve(Object sender, ResolveEventArgs args) in /Users/cameron/code/mono-addins/Mono.Addins/Mono.Addins/AddinEngine.cs:line 324
at System.Runtime.Loader.AssemblyLoadContext.InvokeResolveEvent(ResolveEventHandler eventHandler, RuntimeAssembly assembly, String name)
at System.Reflection.RuntimeAssembly.InternalLoad(AssemblyName assemblyName, StackCrawlMark& stackMark, AssemblyLoadContext assemblyLoadContext, RuntimeAssembly requestingAssembly, Boolean throwOnFileNotFound)
at System.Reflection.TypeNameParser.ResolveAssembly(String assemblyName)
at System.Reflection.TypeNameParser.GetType(String typeName, ReadOnlySpan`1 nestedTypeNames, String assemblyNameIfAny)
at System.Reflection.TypeNameParser.Parse()
at System.Reflection.TypeNameParser.GetType(String typeName, Func`2 assemblyResolver, Func`4 typeResolver, Assembly requestingAssembly, Boolean throwOnError, Boolean ignoreCase, Boolean extensibleParser)
at System.Type.GetType(String typeName, Boolean throwOnError)
at Mono.Addins.RuntimeAddin.GetType(String typeName, Boolean throwIfNotFound) in /Users/cameron/code/mono-addins/Mono.Addins/Mono.Addins/RuntimeAddin.cs:line 338
at Mono.Addins.TypeExtensionNode.get_Type() in /Users/cameron/code/mono-addins/Mono.Addins/Mono.Addins/TypeExtensionNode.cs:line 104
at Mono.Addins.TypeExtensionNode.CreateInstance() in /Users/cameron/code/mono-addins/Mono.Addins/Mono.Addins/TypeExtensionNode.cs:line 93
at Mono.Addins.InstanceExtensionNode.GetInstance() in /Users/cameron/code/mono-addins/Mono.Addins/Mono.Addins/InstanceExtensionNode.cs:line 76
at Mono.Addins.ExtensionNodeEventArgs.get_ExtensionObject() in /Users/cameron/code/mono-addins/Mono.Addins/Mono.Addins/ExtensionContext.cs:line 1331
at Pinta.MainWindow.OnExtensionChanged(Object s, ExtensionNodeEventArgs args) in /Users/cameron/code/Pinta/Pinta/MainWindow.cs:line 273