Emit disallowed_names lint for functions

[granddaifuku]

This PR fixes a part of #11306.

Note that disallowed_names still doesn't warn about using disallowed struct (and its field) /module/crate names. I'm planning to address this in a separate PR (if it makes sense to you).

The changes are a bit large, but they primarily involve two updates:

• Enhancing the disallowed_names lint to emit warnings for functions with disallowed names.
• Updating tests that include such functions to explicitly allow the lint.

changelog: [disallowed_names]: Warn on usage of disallowed function names

[rustbot]

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[granddaifuku]

Hi @y21, this PR is ready for review now - could I kindly ask you to take a look when you have a moment? The changes are a bit large, but they primarily involve two updates:

1. Enhancing the disallowed_names lint to emit warnings for functions with disallowed names.
2. Updating tests that include such functions to explicitly allow the lint.

Let me know if you have any questions. Thanks in advance!

[granddaifuku]

Hello @y21, I updated the PR to include the up-to-date master branch.
Would you mind reviewing this PR when you have a moment?
Many thanks!

[rustbot]

☔ The latest upstream changes (possibly f8a3929) made this pull request unmergeable. Please resolve the merge conflicts.

[y21]

Sorry for the long wait. This change makes sense to me, although given the impact on the tests I created a thread on Zulip to see if there's concerns with this: https://rust-lang.zulipchat.com/#narrow/channel/257328-clippy/topic/disallowed_names.20for.20function.20names

Going to leave that for a few days and if nothing comes up then I'd say we're good

[blyxyas]

This should probably ignore functions in testing modules.

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