Create TypeScript style guide

### 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.

Start by reading the existing ESLint configuration and the TypeScript code for extension React components to identify the decisions already made. Document the agreed TypeScript conventions, with particular attention to React component typing, and make the guide suitable for onboarding engineers. Done means the documented guidance reflects the relevant lint rules and covers the requested component-typing choices.

Written by the indexing model from the issue text.