This eliminates a source of bugs if subclasses of `TypeCheckCompletionCallback` forget to call the superclass’s implementation of `sawSolution` from their overridden method.
This hooks up call argument position completion to the typeCheckForCodeCompletion API to generate completions from all the solutions the constraint solver produces (even those requiring fixes), rather than relying on a single solution being applied to the AST (if any).
Co-authored-by: Nathan Hawes <nathan.john.hawes@gmail.com>