RFR: Generate missing null checks [v4]

[Vicente Romero]

> generate missing null checks like for method arguments, return arguments, etc

Vicente Romero has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 15 additional commits since the last revision:

 - Merge branch 'bworld' into generate.missing.null.checks
 - addressing review comments
 - removing NPE for patterns
 - record patterns
 - changes to test
 - Merge branch 'generate.missing.null.checks' of https://github.com/vicente-romero-oracle/valhalla into generate.missing.null.checks
 - recent changes
 - recent changes
 - Merge branch 'bworld' into generate.missing.null.checks
 - more changes
 - ... and 5 more: https://git.openjdk.org/valhalla/compare/6937765e...ef7e0a7d

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1867/files
  - new: https://git.openjdk.org/valhalla/pull/1867/files/02ba9234..ef7e0a7d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1867&range=03
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1867&range=02-03

  Stats: 944 lines in 25 files changed: 391 ins; 451 del; 102 mod
  Patch: https://git.openjdk.org/valhalla/pull/1867.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1867/head:pull/1867

PR: https://git.openjdk.org/valhalla/pull/1867