Directly use IntermediateOutputPath.

Some environments like BenchmarkDotNet set it to an absolute path. Instead of appending it to the project directory, we just use it and hope MSBuild takes care of the rest.

src/Sigourney.Build/build/Sigourney.Build.targets

@@ -8,8 +8,7 @@ https://opensource.org/licenses/MIT
   TreatAsLocalProperty="_SigourneyEnable">
   <Import Project="$(MSBuildThisFileDirectory)Sigourney.PublishMode.targets" />
   <PropertyGroup>
-    <IntermediateDirectory>$(ProjectDir)$(IntermediateOutputPath)</IntermediateDirectory>
-    <ProcessedBySigourney>$(IntermediateDirectory)ProcessedBySigourney</ProcessedBySigourney>
+    <ProcessedBySigourney>$(IntermediateOutputPath)ProcessedBySigourney</ProcessedBySigourney>
     <_SigourneyEnable Condition="$(SigourneyEnable) == false OR $(DesigntimeBuild) == true">false</_SigourneyEnable>
   </PropertyGroup>
 
@@ -21,7 +20,7 @@ https://opensource.org/licenses/MIT
     <ItemGroup>
       <SigourneyConfiguration Include="Sigourney default configuration">
         <SignAssembly>$(SignAssembly)</SignAssembly>
-        <IntermediateDirectory>$(IntermediateDirectory)</IntermediateDirectory>
+        <IntermediateDirectory>$(IntermediateOutputPath)</IntermediateDirectory>
         <KeyOriginatorFile>$(KeyOriginatorFile)</KeyOriginatorFile>
         <AssemblyOriginatorKeyFile>$(AssemblyOriginatorKeyFile)</AssemblyOriginatorKeyFile>
         <References>@(ReferencePath)</References>

src/Sigourney/WeaverConfig.cs

@@ -35,8 +35,8 @@ public class WeaverConfig
         /// <summary>
         /// The "obj/" directory used in the build.
         /// </summary>
-        /// <remarks>It is derieved from the MSBuild
-        /// "IntermediateDirectory" property.</remarks>
+        /// <remarks>It is derieved from the MSBuild "IntermediateOutputPath" property.</remarks>
+        // TODO: Deprecate in the next minor release and replace with IntermediateOutputPath.
         public string? IntermediateDirectory { get; set; }
 
         /// <summary>