Add kokkos tests to CI

[mzuzek]

@mhoemmen @amklinv-nnl @fnrizzi

Changes:

• Add Kokkos builds along Native ones with Kokkos tests executed;
• Build and test in Release and Debug modes (also MDSpan, Kokkos and Kokkos-Kernels);
• Refactoring:
  • reduced/simplified jobs and removed artifact exchange to save time job setup (native workflow execution time dropped from 4m to 1m, and Kokkos workflow takes about 2.5m);
  • container no longer required as bare ubuntu-latest offers GCC 10.3.0 and new CMake (image amklinv/stdblas:latest can't be used anymore because it has CMake 3.13.4 while Kokkos requires 3.16+)

Kokkos testing

Kokkos builds make Kokkos execution policy the default one with LINALG_ENABLE_KOKKOS_DEFAULT=ON, which leads to native tests executing Kokkos implementations and eventually yielding different results than in Native builds.

We could consider extending this one-way cross-testing to Kokkos tests executing the serial implementation - if they were called with serial execution policy (they explicitly use KokkosKernelsSTD::kokkos_exec<>(), so they only test Kokkos implementations now).

[mzuzek]

@mhoemmen @fnrizzi

Let me open this PR for review: the script is pretty much drafted and test failures are not caused by it, so they may addressed on separate, dedicated issues and PRs:

• Fixed:
  • gemm (SEGFAULT): https://github.com/kokkos/stdBLAS/pull/222
  • hemm & symm (SEGFAULT): #209 (connects headers with Kokkos implementations)
  • matrix_inf_norm (Failed): https://github.com/kokkos/stdBLAS/pull/229
  • trmm: #226
  • SEGFAULT fixed by #221
  • numerical nan errors fixed by https://github.com/kokkos/stdBLAS/pull/227
• TODO:
  • norm2 (Failed): TODO #224
  • trmm: #226 - View crashes