When running on TypeScript files, the basic eslint no-unused-vars plugin

is replaced by a TS version, which didn't have any configuration. This

was causing errors on things like unused function parameters, which we

don't want (we often declare function signatures in parent classes which

are implemented in child classes).
This change adds the necessary configuration for this to work.

Saw that I no longer got errors about unused function parameters when

working with TypeScript files.