Prevent duplicate entries in _SourceItemsToCopyToPublishDirectory*

[BrzVlad]

We can end up with duplicated items if they exist both in child projects as well as in the current project that we are building. These end up added to ResolvedFileToPublish and later on passed to crossgen2, which doesn't accept duplicate assembly inputs.

[BrzVlad]

Not entirely sure if this is the right fix since I don't have experience in the area. Obviously this could also be fixed at the level of the ready to run command but handling it here seemed more appropriate. For a more detailed description of the issue and a simple repro see https://github.com/BrzVlad/repros/tree/main/composite-r2r-publish.

Issue encountered while working on composite R2R configuration for BenchmarkDotNet.

[Copilot]

Pull request overview

This PR adds duplicate prevention for _NoneWithTargetPath items when copying to the publish directory. The changes prevent duplicate entries that can occur when items exist in both child projects and the current project, which would later cause crossgen2 to fail when it receives duplicate assembly inputs.

Key changes:

• Add KeepDuplicates attribute to three _NoneWithTargetPath ItemGroup declarations
• Use the existing _GCTPDIKeepDuplicates property (set to false) to control deduplication behavior
• Follow the same pattern already applied to child project items from _AllChildProjectPublishItemsWithTargetPath