v2.1.0-rc.3

Changes since v2.1.0-rc.2

• fix(preview): advance the camera while a screen frame is held
• fix(timeline): copy a whole pill, not the fragment clicked
• fix(compositor): read the macOS preview back through Managed textures on Intel Macs
• fix(preview): give a shared frame's slot back 40 ms after Chromium lets go
• fix(preview): eight ring slots, and a slow display's two frames as the hold floor
• test(compositor): the stale-ready test holds every slot but the last, whatever the ring size

Full Changelog: v2.1.0-rc.2...v2.1.0-rc.3