[Optix] - Add runnable integration tests with optix backend.

[szihs]

Right now the slang-rhi tests only cover couple of raytracing tests. But we want to improve the coverage for the SER and LSS work

.\build\external\slang-rhi\Debug\slang-rhi-tests.exe -tc=ray-tracing
[doctest] doctest version is "2.4.11"
[doctest] run with "--help" for options
===============================================================================
[doctest] test cases: 0 | 0 passed | 0 failed | 145 skipped
[doctest] assertions: 0 | 0 passed | 0 failed |
[doctest] Status: SUCCESS!
[doctest] doctest version is "2.4.11"
[doctest] run with "--help" for options
-------------------------------------------------------------------------------
ray-tracing-a
ray-tracing-a (d3d11)                                             DONE (0.82s)
ray-tracing-a (d3d12)                                             DONE (1.20s)
ray-tracing-a (vulkan)                                            DONE (2.00s)
ray-tracing-a (metal)                                             DONE (0.00s)
ray-tracing-a (cpu)                                               DONE (6.67s)
ray-tracing-a (cuda)                                              DONE (3.47s)
ray-tracing-a (wgpu)                                              DONE (0.00s)
ray-tracing-a                                                   PASSED (14.18s)
===============================================================================
[doctest] test cases:  1 |  1 passed | 0 failed | 144 skipped
[doctest] assertions: 56 | 56 passed | 0 failed |
[doctest] Status: SUCCESS!
[doctest] doctest version is "2.4.11"
[doctest] run with "--help" for options
-------------------------------------------------------------------------------
ray-tracing-b
ray-tracing-b (d3d11)                                             DONE (0.86s)
ray-tracing-b (d3d12)                                             DONE (1.12s)
ray-tracing-b (vulkan)                                            DONE (1.16s)
ray-tracing-b (cpu)                                               DONE (4.71s)
ray-tracing-b (cuda)                                              DONE (2.57s)
ray-tracing-b (wgpu)                                              DONE (0.00s)
ray-tracing-b                                                   PASSED (10.44s)
===============================================================================
[doctest] test cases:  1 |  1 passed | 0 failed | 144 skipped
[doctest] assertions: 56 | 56 passed | 0 failed |
[doctest] Status: SUCCESS!

We need to add more tests.