[master] RFR: OMWorld: Cleanup BasicLock header

[Axel Boldt-Christmas]

Cleanup the usage of the header field in BasicLock. Because the asserts are stronger now I also cleanup the zero usage of the BasicLock. Because https://bugs.openjdk.org/browse/JDK-8307532 is not yet implemented I have not tested this interaction but as this now restricts the displaced header in the BasicLock to only LM_LEGACY something had to be done for LM_MONITOR support. 

This also changes symbols exposed through JVMCI so it may take extra effort to get this through. 

Similarly to #161 some changes could be upstreamed, and here there is already a distinction as neither `LM_LIGHTWEIGHT` nor `LM_MONITOR` uses the displaced header.

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Commit messages:
 - BasicLock Restructure (includes JVMCI and zero changes)

Changes: https://git.openjdk.org/lilliput/pull/162/files
  Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=162&range=00
  Stats: 253 lines in 17 files changed: 125 ins; 6 del; 122 mod
  Patch: https://git.openjdk.org/lilliput/pull/162.diff
  Fetch: git fetch https://git.openjdk.org/lilliput.git pull/162/head:pull/162

PR: https://git.openjdk.org/lilliput/pull/162