[Mirror] Legacy View Removal

[csiefer2]

Automated mirror of upstream PR kokkos#9391 This PR removes the legacy View implementation path and consolidates behavior on the non-legacy/mdspan-based path. Most of the churn is deletions (19 files, +82/-6599), including full removal of legacy mapping/atomic/cuda-view internals and related test coverage that targeted legacy ViewMapping/ViewOffset/compile-time subview legality machinery.

Removed Kokkos::Impl symbols (explicitly removed in this PR):

• Kokkos::Impl::DynRankSubviewTag
• Kokkos::Impl::ViewOffset (base template declaration in Kokkos_ViewDataAnalysis.hpp)
• Kokkos::Impl::ViewMapping forward declaration/stub in Kokkos_ViewTraits.hpp and broad usage paths tied to legacy implementation
• Kokkos::Impl::SubviewLegalArgsCompileTime usage/tests removed
• Kokkos::Impl::SubviewExtents usage/tests removed
• Kokkos::Impl::CudaLDGFetch
• Kokkos::Impl::AtomicViewConstTag
• Kokkos::Impl::AtomicDataElement
• Kokkos::Impl::AtomicViewDataHandle
• Kokkos::Impl::ParseViewExtents
• Kokkos::Impl::ApplyExtent
• Kokkos::Impl::_parse_view_extents_impl::* helpers (internal parse machinery)

Header files removed:

• core/src/Cuda/Kokkos_Cuda_View.hpp
• core/src/Kokkos_Extents.hpp
• core/src/View/Kokkos_ViewAtomic.hpp
• core/src/View/Kokkos_ViewLegacy.hpp
• core/src/View/Kokkos_ViewMapping.hpp

Note this doesn't fully prune the code from all #ifdef KOKKOS_ENABLE_IMPL_VIEW_LEGACY yet. I want to get full test coverage first.

[gemini-code-assist]

Caution

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