Rename Package Icon file only when packing

Every "official" .NET packages use 'Icon' as its file name.
Since, the icon file itself is public and older packages refer them by URL,
we only change the file name during packaging which would be in the package.

Author: Nirmal4G

build/Windows.Toolkit.Common.props

@@ -10,7 +10,7 @@
     <Copyright>(c) .NET Foundation and Contributors.  All rights reserved.</Copyright>
     <PackageProjectUrl>https://github.com/windows-toolkit/WindowsCommunityToolkit</PackageProjectUrl>
     <PackageReleaseNotes>https://github.com/windows-toolkit/WindowsCommunityToolkit/releases</PackageReleaseNotes>
-    <PackageIcon>nuget.png</PackageIcon>
+    <PackageIcon>Icon.png</PackageIcon>
     <PackageIconUrl>https://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/master/build/nuget.png</PackageIconUrl>
   </PropertyGroup>
 

build/Windows.Toolkit.Common.targets

@@ -13,7 +13,7 @@
   </PropertyGroup>
 
   <ItemGroup Condition="$(IsPackable)">
-    <None Include="$(BuildToolsDirectory)nuget.png" Pack="true" PackagePath="\" />
+    <None Include="$(BuildToolsDirectory)nuget.png" Pack="true" PackagePath="\Icon.png" />
     <None Include="$(RepositoryDirectory)License.md" Pack="true" PackagePath="\" />
   </ItemGroup>