Bare top-level expressions

Given this module:
```hs
sum [1,2,3,4]
```

We get this error when loading it into GHCi:

```
Main.hs:1:1: error:
Parse error: module header, import declaration
or top-level declaration expected.
|
1 | sum [1,2,3,4]
| ^^^^^^^^^^^^^
Failed, no modules loaded.
```

Perhaps we can:

1. Recognize that this is a bare top-level expression.
2. Reflect that in the error message.
3. Suggest that the user might want to bind this bare expression to a name.

Suggested error message:

```
Main.hs:1:1: error:
Parse error: module header, import declaration
or top-level declaration expected, but encountered
a bare expression instead.
Perhaps you meant to bind this expression to a name?
|
1 | sum [1,2,3,4]
| ^^^^^^^^^^^^^
Failed, no modules loaded.
```

Ideally, it would also be nice if the error message didn't mention module headers or import declarations in places where it doesn't apply, such as in this example:

```hs
import Data.List
xs = [3,5,1,2]
sort xs
```
```
Main.hs:3:1: error:
Parse error: module header, import declaration
or top-level declaration expected.
|
3 | sort xs
| ^^^^^
```