[llvm] [Offload][OMPX] Add the runtime support for multi-dim grid and block (PR #118042)

[Shilei Tian via llvm-commits]

shiltian wrote:

@jplehr I tested it locally but couldn't reproduce the failure locally.

```
➜  clang -fopenmp --offload-arch=gfx1030 llvm-project/offload/test/api/omp_env_vars.c -o main
➜  env OMP_NUM_TEAMS=1 OMP_TEAMS_THREAD_LIMIT=1 LIBOMPTARGET_INFO=16 ./main
"PluginInterface" device 0 info: Launching kernel __omp_offloading_10302_8ee073e_main_l9 with [1,1,1] blocks and [1,1,1] threads in SPMD mode
AMDGPU device 0 info: #Args: 1 Teams x Thrds:    1x   1 (MaxFlatWorkGroupSize: 256) LDS Usage: 56B #SGPRs/VGPRs: 39/32 #SGPR/VGPR Spills: 0/0 Tripcount: 0
```

https://github.com/llvm/llvm-project/pull/118042