ARROW-11168: [Rust] [Doc] Fix cargo doc warnings

[mqy]

The PR fixed cargo doc warnings (including the generated flatbuffer files), and corrected several typos.
To catch all possible cargo doc warnings, it looks like we have to run cargo doc for both nightly and stable.

I had filed an issue https://issues.apache.org/jira/browse/ARROW-11179 to address the cargo doc problem about generated flatbuffer files, hope this can be resolved soon. Currently, the patch is created as format-0ed34c83.patch for regen.sh.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-11168

[jorgecarleitao]

LGTM. Thanks a lot for taking this!

[mqy]

Turn to draft because there are cargo test errors. Back soon.

[mqy]

The build failed, no idea why does it build parquet-format 2.7.0.
I can't reproduce this problem with cargo build --all-targets on my local host with code of this PR.

The merged commit c4ee536 also failed with same error.

The problem is filed at https://issues.apache.org/jira/browse/ARROW-11184

@nevi-me I saw you just released parquet-format 2.7.0 hours ago, any idea?

[nevi-me]

We released parquet-format-rs:2.7.0 today. If it's breaking this build, then it's likely going to break others. I'll have a look, and pin versions if needed.

[alamb]

As pointed out by @carols10cents , this appears to have failed on master too: https://github.com/apache/arrow/actions?query=branch%3Amaster+workflow%3ARust

https://github.com/apache/arrow/actions/runs/471629105

[alamb]

I'll look into this and try and get the build passing again

[nevi-me]

@alamb I've opened #9138

[alamb]

This PR probably needs to be rebased to pick up the fix for #9138

[mqy]

LGTM. Thanks a lot for taking this!

@jorgecarleitao thanks for the review. It seems the CI is getting close to success, please review again.

[alamb]

FWIW I tested this branch out locally and it worked really nicely -- no more warnings during build. Thanks @mqy !