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: I2c318f6f51107cd80f0c70531e23f73569b0ec83
