Fixes #7925

Summary of Changes

• Change instances of source maps to use typeof SourceMaps instead of any/Object
• Add a couple more types to address flow inference issue (see below)

Considerations

I couldn't find a way to import the typeof the default export of a module alongside named imports from the same module.

import typeof SourceMaps, { isGeneratedId } from "devtools-source-map";

Originally, I included two imports and suppressed the eslint error but changed when I realized the frequency this would be required. The current approach is to import the default export and use typeof in the instance typing later.

import typeof SourceMaps, { isGeneratedId } from "devtools-source-map";
// later
const sourceMaps: typeof SourceMaps = ...;

I also ran into a couple issues that seem to trace back to flow. I've documented them inline but noting them here for traceability in GitHub.

Explicitly typing an array wrapped by a Promise
facebook/flow#5294

Unable to correctly type the result of a spread on a union type.
facebook/flow#7298