RFR: 8310905: [lw5] addressing review comments on null restricted types [v3]

[Vicente Romero]

> addressing some review comments related to PR [1]
> 
> [1] https://github.com/openjdk/valhalla/pull/872

Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:

  adding more methods to NullabilityComparator visitor, adding more test cases

-------------

Changes:
  - all: https://git.openjdk.org/valhalla/pull/880/files
  - new: https://git.openjdk.org/valhalla/pull/880/files/dd3fcccf..b605e9ce

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=880&range=02
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=880&range=01-02

  Stats: 186 lines in 3 files changed: 177 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/valhalla/pull/880.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/880/head:pull/880

PR: https://git.openjdk.org/valhalla/pull/880