Rollup merge of #144649 - estebank:issue-144602, r=lcnr

Account for bare tuples and `Pin` methods in field searching logic

When looking for the field names and types of a given type, account for tuples. This allows suggestions for incorrectly nested field accesses and field name typos to trigger as intended. Previously these suggestions only worked on `ty::Adt`, including tuple structs which are no different to tuples, so they should behave the same in suggestions.

When suggesting field access which would encounter a method not found, do not suggest pinning when those methods are on `impl Pin` itself.

```
error[E0599]: no method named `get_ref` found for tuple `(BufReader<File>,)` in the current scope
  --> $DIR/missing-field-access.rs:11:15
   |
LL |     let x = f.get_ref();
   |               ^^^^^^^ method not found in `(BufReader<File>,)`
   |
help: one of the expressions' fields has a method of the same name
   |
LL |     let x = f.0.get_ref();
   |               ++
```
instead of
```
error[E0599]: no method named `get_ref` found for tuple `(BufReader<File>,)` in the current scope
  --> $DIR/missing-field-access.rs:11:15
   |
LL |     let x = f.get_ref();
   |               ^^^^^^^ method not found in `(BufReader<File>,)`
   |
help: consider pinning the expression
   |
LL ~     let mut pinned = std::pin::pin!(f);
LL ~     let x = pinned.as_ref().get_ref();
   |
```

Fix rust-lang/rust#144602.

Author: tgross35