RFR: Update parser tests

[Maurizio Cimadamore]

This PR updates the parser tests to reflect the latest changes in the programming model.
This led to minor parser tweaks to javac parser, to make sure that sensible error messgaes were being reported when null-restricted types are used in the wrong place.

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Commit messages:
 - Update parser tests

Changes: https://git.openjdk.org/valhalla/pull/1847/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1847&range=00
  Stats: 707 lines in 6 files changed: 295 ins; 397 del; 15 mod
  Patch: https://git.openjdk.org/valhalla/pull/1847.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1847/head:pull/1847

PR: https://git.openjdk.org/valhalla/pull/1847