[foreign-preview] RFR: 8282070: Drop workaround from memory segment implementation [v2]

[Maurizio Cimadamore]

> Following some preliminary experiments (see [1]) it is now finally time to drop the various workarounds we have in the memory segment implementation. This patch removes two workarounds:
> 
> * special treatment for "small" segments (e.g. segments whose size fits in an int) - see `MemorySegment::isSmall`; these segments were special cased so that bound checks would only involve `int` comparisons. This has now been fixed in JDK-8276116, and special treatment is no longer required.
> 
> * special shortcuts to avoid extra alignment checks. Since when generating var handles from a layout we check most of the alignment constraints (except those involving the base address), in the past we have added a fastpath for these var handles, as C2 had trouble hoisting alignment checks outside of the loops. This has now been fixed in JDK-8277850 and is no longer required.
> 
> I have run benchmarks before and after and got identical results. Some benchmarkks in `ParallelSum` got a boost, but those always have noise, due to multi-threading.

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Address review comments:
  * inlined Utils::scaleOffset into callsites
  * drop redundant check from AbstractMemorySegment::checkBounds

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/644/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/644/files/ea2d79ec..a5fbef94

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=644&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=644&range=00-01

  Stats: 36 lines in 3 files changed: 14 ins; 7 del; 15 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/644.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/644/head:pull/644

PR: https://git.openjdk.java.net/panama-foreign/pull/644