[master] RFR: 8301562: [Lilliput] Runtime flag to enable Lilliput

[Roman Kennke]

This change introduces an experimental runtime flag -XX:[+/-]UseCompactObjectHeaders which can be used to disable Lilliput. The flag guards all the relevant places that directly affect the object layout and the accesses to Klass* etc. The change also restores the previous behaviour when -UseCompactObjectHeaders is selected.

Testing:
 - [x] tier1 (x86_64, x86_32, aarch64) +UseCompactObjectHeaders
 - [x] tier2 (x86_64, x86_32, aarch64) +UseCompactObjectHeaders
 - [x] tier1 (x86_64, x86_32, aarch64) -UseCompactObjectHeaders
 - [x] tier2 (x86_64, x86_32, aarch64) -UseCompactObjectHeaders

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Commit messages:
 - Use tbz instruction in load_nklass to avoid touching live flags in verify_oop stub
 - Comment-out mis-placed assert
 - Only iterate metadata when not using compact object headers in SA
 - Problem-list CompressedClassSpaceSize test
 - Fix TestMetaspacePerfCounters test
 - Fix BaseOffsets.java test
 - Revert condition to turn off CDS when Lilliput is disabled
 - Make UseCompactObjectHeaders default to on
 - Fix intendation
 - Revert change in TestMetaspacePerfCounters test
 - ... and 32 more: https://git.openjdk.org/lilliput/compare/7ed8bfa6...becf81c0

Changes: https://git.openjdk.org/lilliput/pull/70/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=70&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301562
  Stats: 979 lines in 63 files changed: 631 ins; 70 del; 278 mod
  Patch: https://git.openjdk.org/lilliput/pull/70.diff
  Fetch: git fetch https://git.openjdk.org/lilliput pull/70/head:pull/70

PR: https://git.openjdk.org/lilliput/pull/70