[master] RFR: 8347710: [Lilliput] Implement 4 byte headers

[Roman Kennke]

Packs/reduces header bits to just 4 bytes.

This reduces the number of Klass* bits to 19 bits, which allows for ~500,000 classes.

Testing:

- tier1 (-UCOH)
- tier2 (-UCOH)
- tier1 (+UCOH)
- tier2 (+UCOH)

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

Commit messages:
 - Merge branch 'JDK-8320761' into JDK-8347710
 - Merge branch 'JDK-8346011' into JDK-8320761
 - Make all constants constexpr
 - 8347710: [Lilliput] Implement 4 byte headers
 - 8320761: [Lilliput] Implement compact identity hashcode
 - 8346011: [Lilliput] Compact Full-GC Forwarding

Changes: https://git.openjdk.org/lilliput/pull/193/files
  Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=193&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8347710
  Stats: 2295 lines in 132 files changed: 1312 ins; 667 del; 316 mod
  Patch: https://git.openjdk.org/lilliput/pull/193.diff
  Fetch: git fetch https://git.openjdk.org/lilliput.git pull/193/head:pull/193

PR: https://git.openjdk.org/lilliput/pull/193