Upgrade to TS 2.8

[forabi]

TypeScript 2.8 has a pretty cool feature, called Conditional Types, that allows us to do type-level programming, including things like:

• Excluding keys from object types with the new built-in Exclude<T, U>
• Unboxing types wrapped in promises like this: type UnboxPromise<T> = T extends Promise<infer R> ? R : T
• Getting the return type of a function with the new built-in ReturnType<T>.
• Removing null and undefined from types, with the new built-in NonNullable<T>.

NonNullable is particularly useful for us because we can get rid of non-null assertions in components that consume API queries that could possibly have a null value. See the diff to get an idea of how this could simplify our types.

Not merging this for now because:

• TypeScript 2.8 is not stable yet, will be released this month.
• typescript-eslint-parser is failing on the new infer R and T extends R ? ... syntax.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@ea4dd75). Click here to learn what that means.
The diff coverage is 80.76%.

@@            Coverage Diff            @@
##             master     #342   +/-   ##
=========================================
  Coverage          ?   80.19%           
=========================================
  Files             ?       90           
  Lines             ?      919           
  Branches          ?      113           
=========================================
  Hits              ?      737           
  Misses            ?      126           
  Partials          ?       56

Impacted Files	Coverage Δ
.../app/pages/NotablePerson/NotablePerson.module.scss	100% <ø> (ø)
.../app/pages/NotablePerson/LoadableNotablePerson.tsx	100% <100%> (ø)
...components/PersonDetails/PersonDetails.module.scss	100% <100%> (ø)
...p/components/EditorialSummary/EditorialSummary.tsx	79.41% <100%> (ø)
.../pages/NotablePerson/NotablePersonBodyDummyData.ts	50% <50%> (ø)
src/app/components/PersonDetails/PersonDetails.tsx	71.42% <72.72%> (ø)
src/app/pages/NotablePerson/NotablePersonBody.tsx	80% <80%> (ø)
src/app/pages/NotablePerson/NotablePerson.tsx	84.37% <86.2%> (ø)

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[forabi]

Hmm, I thought I disabled codecov comments 🤔

Anyway, here are the built-in conditional types that will be available in TS 2.8: microsoft/TypeScript#21847

[wholesomedev]

Dude, this is awesome and just in time. Yesterday I was googling for "typescript how to remove null from type" and now I have my answer!

[forabi]

Yep! Conditional types are very powerful!

[wholesomedev]

🎉