Rename "import jet" to "import kotlin" in Java sources
Revert "Rename "import jet.*" to "import kotlin.*" on ant dist"

This reverts commit 4a5823c5bb53c13624714599774745aaacb93791.
Revert "Add a temporary hack for migration "jet" -> "kotlin""

This reverts commit fb12c56d1ad697fc4989e3f76ce1020180134ad7.
Revert "Suppress "nothing to override" on equals, hashCode, toString"

This reverts commit 640dac834fa23485121e2ad2b6fa20a32a6234c8.
Revert temporary type adjustments on builtins

These were made during migration of builtins from package "jet" to "kotlin"