Create TypeScript style guide

[brad-decker]

Description

Before engineers can divide and conquer on the conversion of files to TypeScript within the extension, we should create a TypeScript style guide that helps us write code that is similar to one another. A great deal of these decisions have been made and are codified in our eslint configuration. However, we should pull these decisions forward from that configuration into a document that will serve to onboard engineers to using TypeScript. A particular amount of focus should be placed on React components and how we'd like those to be typed as there is a number of ways.

[MajorLift]

Related/duplicates:

• Complete TypeScript guidelines contributor-docs#69
• Standards: React style guide / best practices contributor-docs#24
• Create React Best Practices Documentation contributor-docs#1
• Create Redux Best Practices + design goals Document contributor-docs#2