fix: Support auto-import for annotations

[mdiin]

Identify the Bug

#114

Description of the Change

atom-languageclient considers interfaces as being of type mixin, and (many?) annotations are interfaces. Since buildImportSuggestion does not handle the mixin type interfaces cannot be auto-imported.

This change treats interfaces same as classes, which seems to me is the correct behaviour, seeing as interfaces are types without an implementation.

Alternate Designs

I did not consider alternate designs, although I am open to discussion about this fix.

Possible Drawbacks

I see no obvious drawbacks.

Verification Process

• Trigger imports of various types

Release Notes

Fixed an issue where auto-import of interfaces would fail.