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
2038153739,I_kwDOAMm_X855e8IL,8545,map_blocks should dispatch to ChunkManager,35968931,open,0,,,5,2023-12-12T16:34:13Z,2023-12-22T16:47:27Z,,MEMBER,,,,"### Is your feature request related to a problem?

#7019 generalized most of xarrays internals to be able to use any chunked array type that we can create a `ChunkManagerEntrypoint` for. Most functions now go through this (e.g. `apply_ufunc`), but I did not redirect `xarray.map_blocks` to go through `ChunkManagerEntrypoint`.

This redirection works by dispatching to high-level dask.array primitives such as `dask.array.apply_gufunc`, `dask.array.blockwise`, and `dask.array.map_blocks`. However the current implementation of `xarray.map_blocks` is much lower-level, building a custom HLG, so it was not obvious how to swap it out.

### Describe the solution you'd like

I would like to either:

1) Replace the current internals of `xarray.map_blocks` with a simple call to `ChunkManagerEntrypoint.map_blocks`. This would be the cleanest separation of concerns we could do here. Presumably there is some obvious reason why this cannot or should not be done, but I have yet to understand what that reason is. (either @dcherian or @tomwhite can you enlighten me perhaps? 🙏) 

2) (More likely) refactor so that the existing guts of `xarray.map_blocks` are only called from the `ChunkManagerEntrypoint`, and a non-dask chunked array (i.e. cubed, but in theory other types too) would be able to specify how it wants to perform the map_blocks.

### Describe alternatives you've considered

Leaving it as the status quo breaks the nice abstraction and separation of concerns that #7019 introduced.

### Additional context

Split off from https://github.com/pydata/xarray/issues/8414","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/8545/reactions"", ""total_count"": 1, ""+1"": 1, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,issue