Better suggestions for Fn-family trait selection errors

[compiler-errors]

1. Suppress suggestions to add std::ops::Fn{,Mut,Once} bounds when a type already implements Fn{,Mut,Once}
2. Add a note that points out that a type does in fact implement Fn{,Mut,Once}, but the arguments vary (either by number or by actual arguments)
3. Add a note that points out that a type does in fact implement Fn{,Mut,Once}, but not the right one (e.g. implements FnMut, but Fn is required).

Fixes #95147

[rust-highfive]

r? @davidtwco

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[davidtwco]

@bors r+

[bors]

📌 Commit e0c8780 has been approved by davidtwco