RFR: 8318117: [lw5] create a switch for null-restricted types

[Vicente Romero]

switch for opt-in for null restricted types features

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

Commit messages:
 - removing white space
 - 8318117: [lw5] create a switch for null-restricted types

Changes: https://git.openjdk.org/valhalla/pull/940/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=940&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318117
  Stats: 382 lines in 48 files changed: 116 ins; 47 del; 219 mod
  Patch: https://git.openjdk.org/valhalla/pull/940.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/940/head:pull/940

PR: https://git.openjdk.org/valhalla/pull/940