This PR causes Lean to search through `@[suggest_for]` annotations on
certain errors that look like unknown identifiers that got incorrectly
autobound. This will correctly identify that a declaration of type
`Maybe String` should be `Option String` instead.
## Example
```
example : Except String Unit := return .ok ()
```
```
Function expected at
Result
but this term has type
?m.1
Note: Expected a function because this term is being applied to the argument
String
Hint: The identifier `Result` is unknown, and Lean's `autoImplicit` option causes an unknown identifier to be treated as an implicitly bound variable with an unknown type. However, the unknown type cannot be a function, and a function is what Lean expects here. This is often the result of a typo or a missing `import` or `open` statement.
Perhaps you meant `Except` in place of `Result`?
```
The last line is added by this PR.
We must search the environment extension first, and then the builtin
table. Otherwise, the builtin declarations do not change when we
modify the files.
closes#1021
