[typescript] Move @types/jss from devDependencies to dependencies

[pelotom]

#9678 added a devDependency on @types/jss, however it exposes types obtained from JSS to consumers of Material UI, so it should really be a dependency. Currently one has to add a dependency on @types/jss to one's own project or the Material UI dependency doesn't type check.

[oliviertassinari]

This @types dependency question has been raised by @rosskevin in the past. My concern was about bloating the node_modules for people no relying on TypeScript. To benchmark with how the other libraries are handling the issue.

[pelotom]

That's an understandable concern, but @types/jss is pretty lightweight (as are most typings-only packages).

> du -h node_modules/\@types/jss
 16K	node_modules/@types/jss

[rosskevin]

After spending more time on this particular subject, I feel like all @types for runtime code should be in dependencies. Typescript projects require them just like the dependency itself, so this just makes trial and error work for TS users.

As a counter argument to the bloat argument:

• it's a single top level folder
• @types have very few files
• these are never included in the bundle

So I see no reason to avoid type in dependencies.