Update dependencies from https://github.com/dotnet/winforms build 20200226.1 (#2656)

- Microsoft.Private.Winforms - 5.0.0-preview.2.20126.1

eng/Version.Details.xml

 <?xml version="1.0" encoding="utf-8"?>
 <Dependencies>
   <ProductDependencies>
-    <Dependency Name="Microsoft.Private.Winforms" Version="5.0.0-preview.2.20125.5">
+    <Dependency Name="Microsoft.Private.Winforms" Version="5.0.0-preview.2.20126.1">
       <Uri>https://github.com/dotnet/winforms</Uri>
-      <Sha>9add3012e98d9a3e8abbb6d48baf828abae23ad2</Sha>
+      <Sha>fb0aeb35d816c8ecb4085443b94568e2ee89aff3</Sha>
     </Dependency>
   </ProductDependencies>
   <ToolsetDependencies>

eng/Versions.props

@@ -9,7 +9,7 @@
   </PropertyGroup>
   <!-- NuGet Package Versions -->
   <PropertyGroup>
-    <MicrosoftPrivateWinformsVersion>5.0.0-preview.2.20125.5</MicrosoftPrivateWinformsVersion>
+    <MicrosoftPrivateWinformsVersion>5.0.0-preview.2.20126.1</MicrosoftPrivateWinformsVersion>
   </PropertyGroup>
   <!-- Packages that come from https://github.com/dotnet/coreclr -->
   <PropertyGroup>