RFR: 8315880: change LockingMode default from LM_LEGACY to LM_LIGHTWEIGHT

[Daniel D. Daugherty]

Change the default of LockingMode to LM_LIGHTWEIGHT from LM_LEGACY.

This fix has been tested with 3 Mach5 Tier[1-8] runs and a 4th is in process.

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

Commit messages:
 - 8315880: change LockingMode default from LM_LEGACY to LM_LIGHTWEIGHT

Changes: https://git.openjdk.org/jdk/pull/15797/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15797&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315880
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15797.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15797/head:pull/15797

PR: https://git.openjdk.org/jdk/pull/15797