Sync upstream winui3/main - 2026-01-05 (#11)

* Syncing content from committish 8355d5e6d13b992f5d6f54183a5f8aa73e214488

* Syncing content from committish 1e9018ac05740620c1287c25f283fb875807c9a7

* Syncing content from committish a6625368bd42ef1785800dab0c0106bf02098fea

* Syncing content from committish 61ed270500566d622741a76839c7b2f02644a655

* Syncing content from committish 42ac060add60abdd41be8acae220f50400292bb7

* Syncing content from committish 9105d4a85fee1a83abe81c589c3ecbc4856ec9d3

* Merged PR 14476899: Enable warning level 4
Merged PR 14480580: [OSS] Scrubbing unittest code under /dxaml/xcp/components/AccessKeys/*

Syncing content from committish 33029ab13d861e9a1641737e1617041789f34778

---------

Co-authored-by: reunion-maestro-bot <reunion-maestro-bot@microsoft.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: 3 people

src/Directory.Build.props

@@ -19,6 +19,7 @@
     <WindowsAppSDKVerifyWinrtRuntimeVersion>false</WindowsAppSDKVerifyWinrtRuntimeVersion>
     <!-- The sln files in this repo are not always "complete", but we still want to ensure Configuration/Platform are inherited correctly, in particular for graph builds. -->
     <ShouldUnsetParentConfigurationAndPlatform>false</ShouldUnsetParentConfigurationAndPlatform>
+    <WarningLevel>4</WarningLevel>
   </PropertyGroup>
 
   <!-- Import LKG VC Toolset, if enabled (LkgVcTools* env vars set)-->

src/eng/Version.Details.xml

@@ -6,7 +6,7 @@
       <Uri>https://dev.azure.com/microsoft/LiftedIXP/_git/DCPP</Uri>
       <Sha>547b4bb04a27a7e09e61022dc6ac3595fa1550f7</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.WindowsAppSDK.Foundation.TransportPackage" Version="2.0.0-20251224.1.nightly.internal">
+    <Dependency Name="Microsoft.WindowsAppSDK.Foundation.TransportPackage" Version="2.0.0-20251228.0.nightly.internal">
       <Uri>https://dev.azure.com/microsoft/ProjectReunion/_git/WindowsAppSDK</Uri>
       <Sha>7bafcc2d5e3b80e2e1e0b0d160ec7e09cbe94a88</Sha>
     </Dependency>
@@ -23,7 +23,7 @@
       <Uri>https://dev.azure.com/microsoft/ProjectReunion/_git/WindowsAppSDKAggregator</Uri>
       <Sha>eda4bbdc05ddd6d1bc197ff930af59b4e50d891d</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.WindowsAppSDK.Foundation" Version="2.0.251224001-experimental">
+    <Dependency Name="Microsoft.WindowsAppSDK.Foundation" Version="2.0.251228000-experimental">
       <Uri>https://dev.azure.com/microsoft/ProjectReunion/_git/WindowsAppSDK</Uri>
       <Sha>7bafcc2d5e3b80e2e1e0b0d160ec7e09cbe94a88</Sha>
     </Dependency>