This PR reverts all changes to subtyping and cast conversion, meaning that assigning `null` to a null-restricted type is no longer an error. I've resurrected the lint `null` category, to issue a warning in such cases.
There's some stuff left to do, as I realized that the compiler swallows null markers when emitting diagnostics. This is due to a conundrum in the diagnostic formatter calling `stripMetadata`, and that resulting in _all_ metadata (not just type annos) to be lost. ------------- Commit messages: - Remove spurious changes - Revert changes to stripMetadata & friends - Initial push Changes: https://git.openjdk.org/valhalla/pull/1872/files Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1872&range=00 Stats: 208 lines in 11 files changed: 138 ins; 49 del; 21 mod Patch: https://git.openjdk.org/valhalla/pull/1872.diff Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1872/head:pull/1872 PR: https://git.openjdk.org/valhalla/pull/1872
