[llvm] [mlir] [mlir][mesh, shard] Fixing misnomers in mesh dialect (PR #150177)

[Rolf Morel via llvm-commits]

https://github.com/rolfmorel approved this pull request.

Only spot checked a bit but in general makes sense to me. 👍 

Just three remarks, all related to the dialect changing name:
1. I would prefer if the commit's title/short message mentions changing the dialect's name.
2. Given that the dialect is changing name, its probably prudent to issue a PSA on the forums (just in case there are some users out there and to document that this is a thing that happened).
3. Its probably nice to have a message near the top of the dialect's documentation page saying that this dialect used to be called "mesh". Just in case people see this "new" dialect show up and want to figure how it got in.

https://github.com/llvm/llvm-project/pull/150177