[master] RFR: OMWorld: ObjectMonitor:enter

[Axel Boldt-Christmas]

This restructures `ObjectMonitor:enter` to fit better with the `LightweightSynchronizer`. Some parts of this could be upstreamed separately. 

This effectively splits up `ObjectMonitor::enter` into three parts. Which LightweightSynchronizer can weave into its `inflate_and_enter`. 

```c++
bool ObjectMonitor::enter(JavaThread* current) {
  // 1. Spinning without blocking out deflation
  if (spin_enter(current)) {
    return true;
  }

  // 2. Try to block deflation
  ObjectMonitorContentionMark contention_mark(this);
  if (enter_is_async_deflating()) {
    return false;
  }

  // 3. Enter while blocking out deflation
  enter_with_contention_mark(current, contention_mark);
  return true;
}


It may be worth the effort to document these new methods, and also add better documentation to `inflate_and_enter` which describes the invariants and how `ObjectMonitorContentionMark`, markWord transitions and ObjectMonitor::_owner field (on newly inserted monitors) plays together to guarantee correctness and works. 

This commit is currently based on ffc4c2fd5ba1c28432a5d5e84b8ada95fba7eeb8 without a merge. So GHA is not tested with lilliput. As long as this is mergable without conflicts (and no manual merge is performed) it will also be possible to move this commit down below lilliput on-top of OMWorld directly.

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

Commit messages:
 - Cleanup ObjectMonitor::enter and LightweightSynchronizer::inflate_and_enter
 - Cleanup and fix enter / enter_for distinction

Changes: https://git.openjdk.org/lilliput/pull/159/files
  Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=159&range=00
  Stats: 246 lines in 6 files changed: 119 ins; 58 del; 69 mod
  Patch: https://git.openjdk.org/lilliput/pull/159.diff
  Fetch: git fetch https://git.openjdk.org/lilliput.git pull/159/head:pull/159

PR: https://git.openjdk.org/lilliput/pull/159