[msbuild] refactor BenchmarkDotNet.Weaver.targets to support mobile platforms

Context: dotnet#2929
Context: https://github.com/dotnet/android/blob/4aa9af89102af2e745a8507992187d3c5993d638/Documentation/guides/MSBuildBestPractices.md

In initially testing BenchmarkDotNet with .NET MAUI, I found that the
weaver was not being executed because the `Publish` target is not
called during the build process for Android and iOS projects. I think
the target could actually run much sooner during builds and achieve
better results.

To address this, I refactored the `BenchmarkDotNet.Weaver.targets`
file to run after `CoreCompile` on the `@(IntermediateAssembly)` in
the `obj` directory. This is similar to what other targets do, such as
the XamlC compiler:

https://github.com/dotnet/maui/blob/8224becbb3a8a6bb1caaca4bbe70c56e88875506/src/Controls/src/Build.Tasks/nuget/buildTransitive/netstandard2.0/Microsoft.Maui.Controls.targets#L213-L255

Other general MSBuild improvements:

* Defined an MSBuild property for everything that seems useful. This
  allows consuming projects to configure the behavior (or
  workarounds!) as needed.

* Made the MSBuild target incremental by using inputs and outputs. If
  the `.dll` file is an input, we can write a `.stamp` file as an
  output to indicate that the weaver has already been run for that
  assembly. If the `.dll` file changes, the weaver will run again.

I tested this change with a .NET MAUI on 4 platforms and also the
existing `BenchmarkDotNet.Samples` console app.

Author: jonathanpeppers

src/BenchmarkDotNet.Weaver/buildTransitive/netstandard2.0/BenchmarkDotNet.Weaver.targets

@@ -2,13 +2,27 @@
 <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <UsingTask TaskName="BenchmarkDotNet.Weaver.WeaveAssemblyTask" AssemblyFile="$(MSBuildThisFileDirectory)..\..\tasks\netstandard2.0\BenchmarkDotNet.Weaver.dll" />
 
-  <Target Name="MarkShouldRunWeaveAssemblyTask" AfterTargets="Build">
-    <PropertyGroup>
-      <ShouldRunWeaveAssemblyTask>true</ShouldRunWeaveAssemblyTask>
-    </PropertyGroup>
-  </Target>
+  <PropertyGroup>
+    <ShouldWeaveAssemblies Condition="'$(ShouldWeaveAssemblies)' == ''">true</ShouldWeaveAssemblies>
+    <WeaveAssembliesAfterTargets Condition="'$(WeaveAssembliesAfterTargets)' == ''">CoreCompile</WeaveAssembliesAfterTargets>
+    <WeaveAssembliesBeforeTargets Condition="'$(WeaveAssembliesBeforeTargets)' == ''">CopyFilesToOutputDirectory</WeaveAssembliesBeforeTargets>
+    <WeaveAssemblyPath Condition="'$(WeaveAssemblyPath)' == ''">$(IntermediateOutputPath)$(TargetName)$(TargetExt)</WeaveAssemblyPath>
+    <WeaveAssembliesStampFile Condition="'$(WeaveAssembliesStampFile)' == ''">$(IntermediateOutputPath)BenchmarkDotNetWeaver.stamp</WeaveAssembliesStampFile>
+  </PropertyGroup>
+  
+  <Target Name="WeaveAssemblies"
+      AfterTargets="$(WeaveAssembliesAfterTargets)"
+      BeforeTargets="$(WeaveAssembliesBeforeTargets)"
+      Condition="'$(ShouldWeaveAssemblies)' == 'true'"
+      Inputs="$(WeaveAssemblyPath)"
+      Outputs="$(WeaveAssembliesStampFile)">
+
+    <WeaveAssemblyTask TargetAssembly="$(WeaveAssemblyPath)" />
 
-  <Target Name="WeaveAssemblies" AfterTargets="MarkShouldRunWeaveAssemblyTask" BeforeTargets="Publish" >
-    <WeaveAssemblyTask TargetAssembly="$(TargetDir)$(TargetFileName)" Condition="'$(ShouldRunWeaveAssemblyTask)' == 'true'" />
+    <!-- Create stamp file for incrementality -->
+    <Touch Files="$(WeaveAssembliesStampFile)" AlwaysCreate="true" />
+    <ItemGroup>
+      <FileWrites Include="$(WeaveAssembliesStampFile)" />
+    </ItemGroup>
   </Target>
 </Project>