Check if a function may raise a certain error

[JSAbrahams]

Current Issue

Use the context built using #148

High-level description of the feature

Do a simple check to check whether a function does indeed raise, and only raise, the errors mentioned in its signature.

Description of potential implementation

Check that the errors, and only the errors, are raised by statements: <statement> raises [<Error>]

[JSAbrahams]

Due to the type checker noting what errors may be raised we don't need to explicitly check that the user annotated these errors.

Currently, it appears that this behaviour has actually been fixed, but we should add some tests to confirm this before closing this issue.

[JSAbrahams]

Closing for now since it is assumed that this has been fixed.