New lint: `unnecessary_map_or` (#11796)

Closes https://github.com/rust-lang/rust-clippy/issues/10118

This lint checks `map_or` method calls to check if they can be
consolidated down to something simpler and/or more readable.

For example, the code
```rs
let x = Some(5);
x.map_or(false, |n| n == 5)
```

can be rewritten as
```rs
let x = Some(5);
x == Some(5)
```

In addition, when the closure is more complex, the code can be altered
from, say,
```rs
let x = Ok::<Vec<i32>, i32>(vec![5]);
x.map_or(false, |n| n == [5])
```
into
```rs
let x = Ok::<Vec<i32>, i32>(vec![5]);
x.is_some_and(|n| n == [5])
```

This lint also considers cases where the `map_or` can be chained with
other method calls, and accommodates accordingly by adding extra
parentheses as needed to the suggestion.

changelog: add new lint `unnecessary_map_or`

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