Housekeeping: fody - use FindType for Exception (#1828)

old code for locating the appropriate System.Exception type did not work
when building using dotnet

Author: mdonoughe

src/ReactiveUI.Fody/ModuleWeaver.cs

@@ -27,7 +27,8 @@ public override void Execute()
             var observableAsPropertyWeaver = new ObservableAsPropertyWeaver
             {
                 ModuleDefinition = ModuleDefinition,
-                LogInfo = LogInfo
+                LogInfo = LogInfo,
+                FindType = FindType
             };
             observableAsPropertyWeaver.Execute();
 

src/ReactiveUI.Fody/ObservableAsPropertyWeaver.cs

@@ -31,6 +31,11 @@ public class ObservableAsPropertyWeaver
         /// </value>
         public Action<string> LogInfo { get; set; }
 
+        /// <summary>
+        /// Locates a type from referenced assemblies by name.
+        /// </summary>
+        public Func<string, TypeDefinition> FindType { get; internal set; }
+
         /// <summary>
         /// Executes this property weaver.
         /// </summary>
@@ -61,10 +66,7 @@ public void Execute()
             var observableAsPropertyHelper = ModuleDefinition.FindType("ReactiveUI", "ObservableAsPropertyHelper`1", reactiveUI, "T");
             var observableAsPropertyAttribute = ModuleDefinition.FindType("ReactiveUI.Fody.Helpers", "ObservableAsPropertyAttribute", helpers);
             var observableAsPropertyHelperGetValue = ModuleDefinition.ImportReference(observableAsPropertyHelper.Resolve().Properties.Single(x => x.Name == "Value").GetMethod);
-            var systemRuntimeName = ModuleDefinition.AssemblyReferences.FirstOrDefault(x => x.Name == "System.Runtime");
-            var exceptionDefinition = systemRuntimeName == null
-                ? ModuleDefinition.ImportReference(typeof(Exception)).Resolve() // Referenced from .NET Framework
-                : ModuleDefinition.AssemblyResolver.Resolve(systemRuntimeName).MainModule.Types.First(x => x.Name == "Exception"); // Referenced from .NET Standard
+            var exceptionDefinition = FindType(typeof(Exception).FullName);
             var constructorDefinition = exceptionDefinition.GetConstructors().Single(x => x.Parameters.Count == 1);
             var exceptionConstructor = ModuleDefinition.ImportReference(constructorDefinition);