Avoid reserved identifiers

[dalg24]

• Identifiers starting with two consecutive underscores are reserved in C++ (meaning user-defined program are not allowed to use them)
  e.g.

  batched/dense/impl/KokkosBatched_Axpy_Impl.hpp:16:#ifndef __KOKKOSBATCHED_AXPY_IMPL_HPP__
  batched/dense/impl/KokkosBatched_Axpy_Impl.hpp:17:#define __KOKKOSBATCHED_AXPY_IMPL_HPP__
  

  or

  batched/dense/impl/KokkosBatched_HostLevel_Gemm_Armpl_Impl.hpp:74:  HandleType *const __handle;
  batched/dense/impl/KokkosBatched_HostLevel_Gemm_Armpl_Impl.hpp:80:  AViewType __A;
  batched/dense/impl/KokkosBatched_HostLevel_Gemm_Armpl_Impl.hpp:81:  avt *__Adp = nullptr;
  batched/dense/impl/KokkosBatched_HostLevel_Gemm_Armpl_Impl.hpp:82:  armpl_int_t __Ajstrd, __Aistrd, __Abstrd;
  batched/dense/impl/KokkosBatched_HostLevel_Gemm_Armpl_Impl.hpp:84:  BViewType __B;
  

• Identifiers starting with an underscore followed by an uppercase letter are reserved in C++
  For example

  batched/dense/impl/KokkosBatched_HostLevel_Gemm_Serial_Impl.hpp:131:  BatchedSerialGemm(ScalarType _alpha, AViewType _A, BViewType _B, ScalarType _beta, CViewType _C)
  batched/dense/impl/KokkosBatched_HostLevel_Gemm_Serial_Impl.hpp:132:      : A(_A), B(_B), C(_C), alpha(_alpha), beta(_beta) {}
  

• Avoid defining macros starting with KOKKOS_ (this includes header guards)

  blas/impl/KokkosBlas_util.hpp:18:#define KOKKOS_BLAS_UTIL_HPP
  blas/tpls/KokkosBlas_tpl_spec.hpp:89:#define KOKKOS_CUBLAS_SAFE_CALL_IMPL(call) KokkosBlas::Impl::cublas_internal_safe_call(call, #call, __FILE__, __LINE__)
  

  instead consider doing KOKKOSBLAS_ or KOKKOSKERNELS_BLAS, etc.

[cwpearson]

Most KOKKOS_ macros are either include guards or Impl and we can search/replace, except this one: #2371