Consolidation for self contained, built on #34055 (#34134)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request

First step on self containment. Once #34055 goes in, this number of
modified files should go way down.

Common.Selfcontained.props is the new item and
src/dsc/PowerToys.Settings.DSC.Schema.Generator/PowerToys.Settings.DSC.Schema.Generator.csproj
would be an example of a file that had SelfContained set to true prior
and now that logic was moved into a single file.

<!-- Please review the items on the PR checklist before submitting-->
## 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

<!-- Provide a more detailed description of the PR, other things fixed
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

---------

Co-authored-by: Jaime Bernardo <jaime@janeasystems.com>

src/settings-ui/Settings.UI/PowerToys.Settings.csproj

@@ -1,5 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
-  
+    <!-- Look at Directory.Build.props in root for common stuff as well -->
+    <Import 
+        Condition="exists('$(SolutionDir)src\Common.SelfContained.props')" 
+        Project="$(SolutionDir)src\Common.SelfContained.props" />
+
   <PropertyGroup>
     <OutputType>WinExe</OutputType>
     <TargetFramework>net8.0-windows10.0.20348.0</TargetFramework>
@@ -17,7 +21,6 @@
     <WindowsAppSDKSelfContained>true</WindowsAppSDKSelfContained>
     <!-- OutputPath looks like this because it has to be called both by settings and publish.cmd -->
     <OutputPath>..\..\..\$(Platform)\$(Configuration)\WinUI3Apps</OutputPath>
-    <SelfContained>true</SelfContained>
     <!-- MRT from windows app sdk will search for a pri file with the same name of the module before defaulting to resources.pri -->
     <ProjectPriFileName>PowerToys.Settings.pri</ProjectPriFileName>
   </PropertyGroup>
@@ -33,14 +36,6 @@
     <ApplicationDefinition Include="SettingsXAML\App.xaml" />
   </ItemGroup>
 
-  <!-- SelfContained=true requires RuntimeIdentifier to be set -->
-  <PropertyGroup Condition="'$(Platform)'=='x64'">
-    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
-  </PropertyGroup>
-  <PropertyGroup Condition="'$(Platform)'=='ARM64'">
-    <RuntimeIdentifier>win-arm64</RuntimeIdentifier>
-  </PropertyGroup>
-
   <PropertyGroup Condition="'$(Configuration)'=='Debug'">
     <NoWarn></NoWarn>
     <TreatWarningsAsErrors>True</TreatWarningsAsErrors>