Move fontchain_lint to build/core/tasks

Because `system.img` is a dependency of `fontchain_lint`, and
`system.img` is currently not generated inside `Soong`, it is not
possible to directly convert `fontchain_lint` to `Android.bp`.
Move it to build/core/task first.

Bug: 319050958
Test: m fontchain_lint
Change-Id: Iad483117a609786ecfb885b13015f18dda113155