Make @types/brotli also optional

[newyankeecodeshop]

The types for brotli include a depenency on @types/node. For a web-based user of deck.gl, loaders.gl, and which does not use the brotli library, this adds the node type globals into the type system. That creates some unfortunate inconsistencies with Web/DOM global types.

Since brotli is optional, the types can also be optional so that both can be excluded from environments that don't use them.

[ibgreen]

@newyankeecodeshop I think this is fine, as we don't really expose the brotli API to apps (usage is wrapped in the compression class).

But perhaps we can add the brotli types to devDependencies so that we keep the benefits of type checking while building loaders.gl?