[build] Copy templates to lowercase path on Linux (#5873)

Context: https://github.com/dotnet/sdk/issues/16946

Copy our template workload pack to a lowercase destination so that it
can be detected and used when building and testing on Linux.

Author: pjcollins

build-tools/create-packs/Directory.Build.targets

@@ -122,7 +122,8 @@
         DestinationFolder="$(DotNetPreviewPath)packs\$([System.String]::Copy('%(_WLPacks.Filename)').Replace('.$(_WLPackVersion)', ''))\$(_WLPackVersion)"
     />
     <MakeDir Directories="$(DotNetPreviewPath)template-packs" />
-    <Copy SourceFiles="@(_WLTemplates)" DestinationFolder="$(DotNetPreviewPath)template-packs" />
+    <!-- TODO: Workaround Linux casing issue and copy template packs to lowercase destination -->
+    <Copy SourceFiles="@(_WLTemplates)" DestinationFiles="@(_WLTemplates->'%(Filename)%(Extension)'->ToLower()->'$(DotNetPreviewPath)template-packs\%(Identity)')" />
     <ItemGroup>
       <_UnixExecutables Include="$(DotNetPreviewPath)packs\Microsoft.Android.Sdk.*\*\tools\$(HostOS)\**\*.*" />
       <_FilesToTouch Include="$(DotNetPreviewPath)sdk-manifests\$(DotNetPreviewVersionBand)\Microsoft.NET.Workload.Android\**" />