[web] Add copy-filled icon

Summary:
This icon is required in a design https://linear.app/comm/issue/DES-16/copy-message-button-on-web for copy button on web.

This is in hover state.

Test Plan: Display the icon next to other message actions and check if it is displayed correctly and has appropriate color even when hovering.

Reviewers: atul, kamil, ginsu

Reviewed By: atul, kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D6013