More traits for unary and binary operations

[yasahi-hpc]

This PR aims at adding more traits for unary and binary operations to KokkosFFT_traits.hpp.
This will be applied in another PR to improve error handlings as commented in #80

Following modifications are made

Static assertion to Unary (fftshift, ifftshift) and Binary (Plan and fft functions) APIs. Applications of new traits (unchecked tasks) would be done in another PR.

• Introduce is_view_operatable_v for Unary operation (Views can be accessible from Execspace and the base value types are float/double/Kokkos::complex<float>/Kokkos::complex<double>. In addition, layout is either Kokkos::LayoutLeft or Kokkos::LayoutRight.
• Introduce are_views_operatable_v for Binary operation (Both Views are operatable and have the same precision, layout and rank)
• Introduce have_same_precision_v have_same_base_floating_point_type_v for Binary operation (the values have the same precision base floating point type. For example, float and Kokkos::complex<float> have the same precision)
• Introduce have_same_layout_v for Binary operation
• Introduce have_same_rank_v for Binary operation
• Apply are_views_operatable_v to binary APIs. Exec space and memory space consistency, precision consistency, layout consistency and rank consistency.
• Apply is_view_operatable_v to unary APIs. Exec space and memory space consistency.

[cedricchevalier19]

Looks ok, but I am not sure about the PR description, a lot of items are not checked. I think it is ok to merge if you plan to put the other parts in a separate PR.

[yasahi-hpc]

Looks ok, but I am not sure about the PR description, a lot of items are not checked. I think it is ok to merge if you plan to put the other parts in a separate PR.

Sorry description was unclear. I have updated the description.
As you said, this PR aims to introduce new traits. These traits are then applied in a separate PR.