RFR: 8286756: Cleanup foreign API benchmarks

[Maurizio Cimadamore]

This simple patch regularizes some of the foreign API benchmarks. Some of the changes are:

* use of capital names for var handle and layout constants
* move shared layout and var handle constants in a new superclass, `JavaLayouts`
* regularize aligned vs. unaligned benchmarks, especially in `LoopOverNonConstantHeap`. Since the API now aligns layouts by default, where the benchmark name doesn't say anything we assume aligned layout; for benchmarks that test specifically the use of unaligned layouts, we use the `_unaligned` prefix.

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Commit messages:
 - Fix whitespaces
 - Initial push

Changes: https://git.openjdk.java.net/jdk/pull/8705/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8705&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286756
  Stats: 204 lines in 13 files changed: 54 ins; 69 del; 81 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8705.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8705/head:pull/8705

PR: https://git.openjdk.java.net/jdk/pull/8705