[lworld] RFR: 8248220: [lworld] Optimize empty inline types

[Tobias Hartmann]

The change includes the following optimizations for empty inline types and several bug fixes:
- All uses ((array) loads, stores, allocations, ...) are replaced by the default oop or removed
- Calling convention should not pass/return anything

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Commit messages:
 - Fixed trailing whitespace
 - 8248220: [lworld] Optimize empty inline types

Changes: https://git.openjdk.java.net/valhalla/pull/207/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=207&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248220
  Stats: 372 lines in 19 files changed: 258 ins; 15 del; 99 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/207.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/207/head:pull/207

PR: https://git.openjdk.java.net/valhalla/pull/207