Decide on typescript-eslint project property for 3.0

Created by: ianschmitz

It sounds like setting the project property on typescript-eslint parser options has a significant performance impact (https://github.com/typescript-eslint/typescript-eslint/issues/243). Setting this property is important to enable the use of rules that require type info.

There is one rule we have enabled that i'm not clear if it requires type info or not (@typescript-eslint/no-unused-vars). The TSLint equivalent (https://palantir.github.io/tslint/rules/no-unused-variable/) requires type info.

We should determine whether @typescript-eslint/no-unused-vars requires type info and use this info to decide whether to keep the project property set. There will likely be more rules that we will want to enable down the road that require type info, but hopefully by that time the performance issues will be sorted.