fixed the error message for a user to open the crate

[ibilalkayy]

What does this PR try to resolve?

This PR is resolving an issue where cargo doc --open --examples does not give a clear message when the examples file is given to it.

I changed the message from no crates with documentation in the cargo_doc.rs and doc.rs to requested crate documentation is not available to open. Now it becomes easy for the user to understand what they're missing.

Fixes #14776

How should we test and review this PR?

Here is the command through which you can test this change:

cargo test SNAPSHOTS=overwrite -- doc::open_no_doc_crate

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @epage (or someone else) some time within the next two weeks.

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[Rustin170506]

@ibilalkayy The fmt check failed. You need to run cargo fmt --all.

[ibilalkayy]

Thank you, @Rustin170506! I was not aware of this. Once I get the clarification message from @epage, I will push again.

[epage]

Would you be ok cleaning up the commit history?