Look at adjusted types instead of fn signature types in ptr_arg

[y21]

This simplifies the implementation of the ptr_arg lint a bit and:
Fixes #13308
Fixes #10612

Currently, the lint checks if e.g. a &String parameter is only used in contexts where a &str could work. Part of it worked by looking for path exprs to that parameter in function call position specifically, looking at the callee signature and checking if that parameter type without refs is String (or one of a bunch of other special cases).

This simplified version removes the special casing of function calls and looking at the parameter type and instead just looks at the adjusted type, regardless of the expression it's in. This naturally also covers what the previous version was doing (if the expression is in a function call argument position expecting a &str, then it will have that adjustment. If it requires a &String then it won't have that adjustment and we won't lint).

The linked issue was a FP that happened because the previous implementation simply didn't consider projection types in the signature type, but with this simplification we don't really need to consider that (because we aren't looking at function signatures at all anymore -- the &mut Self::Owned parameter type of clone_into is the already-instantiated and normalized type &mut String).

changelog: none

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[bors]

☔ The latest upstream changes (presumably #13347) made this pull request unmergeable. Please resolve the merge conflicts.

[Centri3]

Looks perfect, just one thing!

[Centri3]

Thanks! @bors r+

[bors]

📌 Commit 15495eb has been approved by Centri3

It is now in the queue for this repository.

[bors]

⌛ Testing commit 15495eb with merge 2536745...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Centri3
Pushing 2536745 to master...