Update to TypeScript 3.3

[aoberoi]

Description

Keep an eye out for how we can improve the usability, specifically using the following feature: microsoft/TypeScript#23893.

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.