[llvm] [Offload] Add olKernelMaxGroupSize (PR #142950)

[Ross Brunton via llvm-commits]

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@@ -276,6 +276,9 @@ struct GenericKernelTy {
                            KernelLaunchParamsTy LaunchParams,
                            AsyncInfoWrapperTy &AsyncInfoWrapper) const = 0;
 
+  virtual Expected<size_t> maxGroupSize(GenericDeviceTy &GenericDevice,
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RossBrunton wrote:

I chose `size_t` since that is consistent with the fields in `ol_kernel_launch_size_args_t` and just generally elsewhere in the API. Happy to change it if explicitly specifying uint64_t is preferred though.

https://github.com/llvm/llvm-project/pull/142950