Decide best practices for typing React props

[victorlin]

With the adoption of TypeScript, there should be a standard way of typing props. This was explored in #1704 and we came up with these options:

1. Define each set of props independently without importing other prop types. This is the simplest approach but results in much code duplication when it comes to prop drilling, especially when each prop has a descriptive docstring.
2. Export individual prop types that are used by a parent. This is what was done in Redesign panel sections in sidebar #1704.
3. Export all props under one type if any are used by a parent. This was considered and evaluated in Redesign panel sections in sidebar #1704 (comment).

[victorlin]

I think (2) is just fine for now, but we might want to keep the door open to other options with increased TypeScript adoption.