issues: 877723396

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
877723396 MDExOlB1bGxSZXF1ZXN0NjMxNjI5NzI2 5271 Ensure `HighLevelGraph` layers are `Layer` instances 11656932 closed 0     1 2021-05-06T16:46:48Z 2021-05-06T20:37:42Z 2021-05-06T20:29:55Z CONTRIBUTOR   0 pydata/xarray/pulls/5271

This PR updates how we construct the HighLevelGraph in subset_dataset_to_block. Currently we create a HighLevelGraph and then manually add a few new layers, which are dicts, directly to hlg.layers.

https://github.com/pydata/xarray/blob/eec2b59bd08498fe3d50d8549b540d0a8409c7ac/xarray/core/parallel.py#L537-L546

However since (in more recent versions of Dask) HighLevelGraph layers are expected to be Layer class instances this can result in unexpected errors (xref https://github.com/pydata/xarray/issues/5077#issuecomment-832359943). Instead of manually adding new layers to hlg.layers, this PR proposes we create a new HighLevelGraph altogether to ensure that hlg.layers won't contain any raw dict layers.

 
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