[lworld] RFR: 8247357: Flattenable field concept needs some cleanup

[Frederic Parain]

Please review these changes cleaning up the flattenable field concept.
The concept has evolved with time and now all fields with an inline type are by definition flattenable, so the need to
have a "flattenable bit" on the side is gone. The changeset contains a mix of renaming and code cleaning. The changes
don't include JIT code, which would be fix in a follow-up patch.

Thank you,

Fred

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Commit messages:
 - Remove flattenable concept and associated code

Changes: https://git.openjdk.java.net/valhalla/pull/77/files
 Webrev: https://webrevs.openjdk.java.net/valhalla/77/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8247357
  Stats: 221 lines in 35 files changed: 12 ins; 51 del; 158 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/77.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/77/head:pull/77

PR: https://git.openjdk.java.net/valhalla/pull/77