[lworld] RFR: 8254258: [lworld] [lw3] Inline types layout can be optimized

[Frederic Parain]

Please review theses changes optimizing fields layout involving small flattened fields.
The patch also includes a fix for the oop map generation of contended field groups.

Tested with Mach5, tier1, tier2, tier3 (no regressions compared to actual status of HEAD).

Thank you,

Fred

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Commit messages:
 - Improve field layout for inline types

Changes: https://git.openjdk.java.net/valhalla/pull/218/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=218&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254258
  Stats: 118 lines in 2 files changed: 53 ins; 33 del; 32 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/218.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/218/head:pull/218

PR: https://git.openjdk.java.net/valhalla/pull/218