[llvm] [Offload] Enable querying a kernel's program (PR #142632)

[Ross Brunton via llvm-commits]

RossBrunton wrote:

@jhuber6 I don't think it's practical to have a single type for both kernels and global variables; the set of legal operations for them is just very different. Even in HSA, which has a shared "symbol" type, the only operation useful to us is querying the symbol's name. I do like the idea of `ol_symbol_t`, but I don't think it maps to GPUs where kernels are not simply function pointers.

https://github.com/llvm/llvm-project/pull/142632