Use RAJADeviceExec consistently

RAJADeviceExec is equal to RAJA::cuda_exec or RAJA::hip_exec or RAJA::omp_parallel_for_exec depending on how we compile. Using RAJADeviceExec everywhere would clean things up and make things more robust for different architectures

Start by searching the repository for uses of RAJA::cuda_exec, RAJA::hip_exec, and RAJA::omp_parallel_for_exec, then compare those call sites with the available RAJADeviceExec definition. Update the relevant execution-policy uses consistently and verify that the project still builds across the supported compilation configurations.

Written by the indexing model from the issue text.