[web] add style prop to icon component

Summary:
we need a style prop to override inline styles the component gives us as defaults. This is a part of the API, I just never added it to the prop types initially.

style prop in icomoon component: https://github.com/aykutkardas/react-icomoon/blob/master/src/index.tsx#L71

Test Plan: We shouldn't have any type errors using the style prop, and the styles in the style prop should work as expected.

Reviewers: atul, ashoat

Reviewed By: atul, ashoat

Subscribers: ashoat, palys-swm, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3346