Making CSWinRt into prop file for c# (#34225)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request

more breaking out stuff

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## PR Checklist

- [ ] **Closes:** #xxx
- [ ] **Communication:** I've discussed this with core contributors
already. If work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end user facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/previewpane/UnitTests-PdfPreviewHandler/UnitTests-PdfPreviewHandler.csproj

@@ -1,25 +1,20 @@
 <Project Sdk="Microsoft.NET.Sdk">
+  <!-- Look at Directory.Build.props in root for common stuff as well -->
+  <Import Project="..\..\..\Common.Dotnet.CsWinRT.props" />
+
   <PropertyGroup>
     <AssemblyTitle>UnitTests-PdfPreviewHandler</AssemblyTitle>
     <AssemblyDescription>PowerToys UnitTests-PdfPreviewHandler</AssemblyDescription>
     <AssemblyTitle>UnitTests-PdfPreviewHandler</AssemblyTitle>
     <Description>PowerToys UnitTests-PdfPreviewHandler</Description>
-  </PropertyGroup>
-
-  <PropertyGroup>
     <ProjectGuid>{ECC20689-002A-4354-95A6-B58DF089C6FF}</ProjectGuid>
     <RootNamespace>PdfPreviewHandlerUnitTests</RootNamespace>
-    <TargetFramework>net8.0-windows10.0.20348.0</TargetFramework>
-    <TargetPlatformMinVersion>10.0.19041.0</TargetPlatformMinVersion>
-    <SupportedOSPlatformVersion>10.0.19041.0</SupportedOSPlatformVersion>
     <ProjectTypeGuids>{3AC096D0-A1C2-E12C-1390-A8335801FDAB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
     <VSToolsPath Condition="'$(VSToolsPath)' == ''">$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)</VSToolsPath>
     <ReferencePath>$(ProgramFiles)\Common Files\microsoft shared\VSTT\$(VisualStudioVersion)\UITestExtensionPackages</ReferencePath>
     <IsCodedUITest>False</IsCodedUITest>
   </PropertyGroup>
 
-  
-
   <ItemGroup>
     <None Remove="HelperFiles\dummy-password.pdf" />
     <None Remove="HelperFiles\dummy.pdf" />
@@ -27,9 +22,6 @@
   </ItemGroup>
 
   <ItemGroup>
-  </ItemGroup>
-  <ItemGroup>
-    <PackageReference Include="Microsoft.Windows.CsWinRT" />
     <PackageReference Include="Moq" />
     <PackageReference Include="MSTest" />
   </ItemGroup>