distinguish the method and associated function diagnostic information
Methods are defined within the context of a struct and their first parameter is always self
Associated functions don’t take self as a parameter
```
modified: compiler/rustc_typeck/src/check/method/suggest.rs
modified: src/test/ui/auto-ref-slice-plus-ref.stderr
modified: src/test/ui/block-result/issue-3563.stderr
modified: src/test/ui/issues/issue-28344.stderr
modified: src/test/ui/suggestions/dont-suggest-pin-array-dot-set.stderr
modified: src/test/ui/suggestions/suggest-methods.stderr
modified: src/test/ui/traits/trait-upcasting/subtrait-method.stderr
```
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