Output the module intermediate files to $(IntDir)Microsoft\cppwinrt\

[YexuanXiao]

This path follows the conventions used by the compiler and the STL (the STL uses the path $(IntDir)Microsoft\STL), avoiding mixing library intermediate files with those of the project files.

The PR also removed CppWinRTModuleLibDir because it appeared in isolation, was unused, and had no explanation.

[Copilot]

Pull request overview

This PR updates the MSBuild targets used by the C++/WinRT NuGet package to place C++20 module intermediate outputs (IFC/object/dependency artifacts) under $(IntDir)Microsoft\cppwinrt\, aligning the output layout with common toolchain conventions and keeping package intermediates separate from project intermediates.

Changes:

• Redirect module compilation outputs for generated .ixx files to $(IntDir)Microsoft\cppwinrt\ via ClCompile item metadata.
• Update the exported module IFC directory (CppWinRTModuleIfcDir) for ProjectReference-based module consumption to match the new location.
• Remove the unused CppWinRTModuleLibDir metadata from CppWinRTGetModuleOutputs.