[main] Source code updates from dotnet/dotnet (#12979)

> [!NOTE]
> This is a codeflow update. It may contain both source code changes
from
> [the VMR](https://github.com/dotnet/dotnet)
> as well as dependency updates. Learn more
[here](https://github.com/dotnet/dotnet/tree/main/docs/Codeflow-PRs.md).

This pull request brings the following source code changes

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## From https://github.com/dotnet/dotnet
- **Subscription**:
[91fa59f1-1864-46b1-b482-87955691317c](https://maestro.dot.net/subscriptions?search=91fa59f1-1864-46b1-b482-87955691317c)
- **Build**:
[20260105.2](https://dev.azure.com/dnceng/internal/_build/results?buildId=2872392)
([296040](https://maestro.dot.net/channel/8298/github:dotnet:dotnet/build/296040))
- **Date Produced**: January 6, 2026 12:20:56 AM UTC
- **Commit**:
[fb2e783fa530d337a56ef5c528a2807b7d63e46d](dotnet/dotnet@fb2e783)
- **Commit Diff**:
[5a69737...fb2e783](dotnet/dotnet@5a69737...fb2e783)
- **Branch**: [main](https://github.com/dotnet/dotnet/tree/main)

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## Associated changes in source repos
-
dotnet/arcade@1c09acb...47a8a69
-
dotnet/aspnetcore@70d8511...1b7269e
-
dotnet/deployment-tools@56c3d96...6ebef72
-
dotnet/efcore@9a86835...5a68c09
-
dotnet/emsdk@f8b8587...36e24b2
-
dotnet/fsharp@3686818...6396a18
-
228caa1...9263fe6
-
NuGet/NuGet.Client@56f4657...cc8f616
-
dotnet/roslyn@a01d6a0...bf35fe5
-
dotnet/runtime@8eb90a6...bce6119
-
dotnet/sdk@65384c6...ec5f7d9
-
dotnet/source-build-reference-packages@d6738f1...a6113e0
-
dotnet/sourcelink@c84e22b...d656e7b
-
dotnet/templating@41ef93a...413680c
-
microsoft/vstest@154e8ba...bbee830
-
dotnet/winforms@1a8c138...01eefd4
-
dotnet/wpf@6e486f4...37b9597

<details>
<summary>Diff the source with this PR branch</summary>

```bash
darc vmr diff --name-only https://github.com/dotnet/dotnet:fb2e783fa530d337a56ef5c528a2807b7d63e46d..https://github.com/dotnet/msbuild:darc-main-2911e53d-2584-4f82-bc52-e50ddaf06f9c
```
</details>

[marker]: <> (End:Footer:CodeFlow PR)

---------

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

Author: dotnet-maestro[bot]

.editorconfig

@@ -415,6 +415,12 @@ dotnet_diagnostic.IDE0301.severity = suggestion
 dotnet_diagnostic.IDE0305.severity = suggestion
 dotnet_diagnostic.IDE0306.severity = suggestion
 
+# Remove unnecessary nullable warning suppression
+dotnet_diagnostic.IDE0370.severity = suggestion
+
+# Remove unnecessary 'unsafe' modifier
+dotnet_diagnostic.IDE0380.severity = suggestion
+
 # Temporarily disable SA1010 "Opening square brackets should not be preceded by a space" until https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3687 is fixed
 dotnet_diagnostic.SA1010.severity = none
 

NuGet.config

@@ -16,6 +16,8 @@
     <add key="dotnet9-transport" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet9-transport/nuget/v3/index.json" />
     <add key="dotnet10" value="https://dnceng.pkgs.visualstudio.com/public/_packaging/dotnet10/nuget/v3/index.json" />
     <add key="dotnet10-transport" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet10-transport/nuget/v3/index.json" />
+    <add key="dotnet11" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet11/nuget/v3/index.json" />
+    <add key="dotnet11-transport" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet11-transport/nuget/v3/index.json" />
     <add key="vs-impl" value="https://pkgs.dev.azure.com/azure-public/vside/_packaging/vs-impl/nuget/v3/index.json" />
   </packageSources>
   <packageSourceMapping>
@@ -49,6 +51,12 @@
     <packageSource key="dotnet10-transport">
       <package pattern="*" />
     </packageSource>
+    <packageSource key="dotnet11">
+      <package pattern="*" />
+    </packageSource>
+    <packageSource key="dotnet11-transport">
+      <package pattern="*" />
+    </packageSource>
   </packageSourceMapping>
   <disabledPackageSources>
     <!--Begin: Package sources managed by Dependency Flow automation. Do not edit the sources below.-->

eng/Version.Details.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Dependencies>
-  <Source Uri="https://github.com/dotnet/dotnet" Mapping="msbuild" Sha="5a69737e6f6447fe397d552503a3909ea49f6f34" BarId="293565" />
+  <Source Uri="https://github.com/dotnet/dotnet" Mapping="msbuild" Sha="fb2e783fa530d337a56ef5c528a2807b7d63e46d" BarId="296040" />
   <ProductDependencies>
     <!-- Necessary for source-build. This allows the live version of the package to be used by source-build. -->
     <Dependency Name="System.CodeDom" Version="9.0.11">