[unnecessary_safety_comment] Some fixes regarding comments above attributes

[teofr]

The way clippy checked for SAFETY comments above attributes was wrong:

• It wasn't considered for items
• It cause an ICE with some attributes
• When considering comments above attributes, it didn't considered comments below them, causing some unlintable situations.

This PR tries to fix this by delegating the skipping of attributes to the function analyzing the source code itself.

changelog: [unnecessary_safety_comment]: Taking into account comments above attributes for items

Fixes #14555
Fixes #15684
Fixes #15754

[github-actions]

Lintcheck changes for c7b79d8

Lint	Added	Removed	Changed
clippy::undocumented_unsafe_blocks	0	18	1
clippy::unnecessary_safety_comment	16	0	2

This comment will be updated if you push new changes

[teofr]

I checked all the removed/added lints and they all make sense to me

• All of the removed undocumented_unsafe_block are correct, and shouldn'te have been there in the first place
• Most of the added unnecesary_safety_comment are because a // SAFETY: comment is used in an unsafe fn. Maybe we should improve the lint message in these cases to suggest a // # Safety comment instead
• One is a SAFETY comment on a struct, which I think is correctly linted
• One is a bug that's been uncovered by this PR but was present already (unnecessary_safety_comment and undocumented_unsafe_blocks visit the same comment twice #15755)
• The changes are a bit strange, basically some notes regarding why the lint is enabled are deleted or added, does anyone know what could cause this?

[rustbot]

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