Update dependencies from https://github.com/dotnet/winforms build 20200720.3 (#3275)

[master] Update dependencies from dotnet/winforms
- Updates:
  - Microsoft.Private.Winforms: from 5.0.0-rc.1.20366.1 to 5.0.0-rc.1.20370.3

eng/Version.Details.xml

 <?xml version="1.0" encoding="utf-8"?>
 <Dependencies>
   <ProductDependencies>
-    <Dependency Name="Microsoft.Private.Winforms" Version="5.0.0-rc.1.20366.1">
+    <Dependency Name="Microsoft.Private.Winforms" Version="5.0.0-rc.1.20370.3">
       <Uri>https://github.com/dotnet/winforms</Uri>
-      <Sha>dec24b8994ced3461036d3fb15ecd16459184ecb</Sha>
+      <Sha>5854f1b352559b04cc4969b0ea2241af517fcdfa</Sha>
     </Dependency>
     <Dependency Name="Microsoft.Win32.Registry" Version="5.0.0-preview.8.20363.2" CoherentParentDependency="Microsoft.Private.Winforms">
       <Uri>https://github.com/dotnet/runtime</Uri>

eng/Versions.props

@@ -9,7 +9,7 @@
   </PropertyGroup>
   <!-- NuGet Package Versions -->
   <PropertyGroup>
-    <MicrosoftPrivateWinformsVersion>5.0.0-rc.1.20366.1</MicrosoftPrivateWinformsVersion>
+    <MicrosoftPrivateWinformsVersion>5.0.0-rc.1.20370.3</MicrosoftPrivateWinformsVersion>
   </PropertyGroup>
   <!-- Packages that come from https://github.com/dotnet/coreclr -->
   <PropertyGroup>