Adopt TS 3.8.x

[mjbvz]

Tracks picking up TypeScript 3.8.x (like 3.8.4 or 3.8.5) for the March iteration. This TypeScript release will be focused on bug fixes

[vscode-triage-bot]

Invalid test plan item. See errors below and the test plan item spec for more information. This comment will go away when the issues are resolved.

Error: Test plan item should have header

[mjbvz]

Closing as no 3.8.x recovery build has been required