MonoAOTLLVMCsProj.txt: Add auto-imports for extension props/targets

Automatically import any `$projectName.Mono.props`, and
`$projectName.Mono.targets` files, if found.

- This allows the actual project to control settings for the generated
project, eg, for modifying the build to add a property like
`SelfContained=true`.

Wasm projects have the same extension mechanism in
`src/BenchmarkDotNet/Templates/WasmCsProj.txt` .

Author: radical

src/BenchmarkDotNet/Templates/MonoAOTLLVMCsProj.txt

@@ -1,5 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk" DefaultTarget="Publish">
   <PropertyGroup>
+    <OriginalCSProjPath>$CSPROJPATH$</OriginalCSProjPath>
+    <MonoPropsPath>$([System.IO.Path]::ChangeExtension('$(OriginalCSProjPath)', '.Mono.props'))</MonoPropsPath>
+    <MonoTargetsPath>$([System.IO.Path]::ChangeExtension('$(OriginalCSProjPath)', '.Mono.targets'))</MonoTargetsPath>
     <OutputType>Exe</OutputType>
     <OutputPath>bin</OutputPath>
     <TargetFramework>$TFM$</TargetFramework>
@@ -13,6 +16,8 @@
     <StartupObject>BenchmarkDotNet.Autogenerated.UniqueProgramName</StartupObject>
   </PropertyGroup>
 
+  <Import Project="$(MonoPropsPath)" Condition="Exists($(MonoPropsPath))" />
+
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Runtime.MonoAOTCompiler.Task" version="6.0.0-*" GeneratePathProperty="true" />
   </ItemGroup>
@@ -75,4 +80,5 @@
 
    </Target>
 
+  <Import Project="$(MonoTargetsPath)" Condition="Exists($(MonoTargetsPath))" />
 </Project>