RFR: 8350118: Simplify the layout access VarHandle [v6]

[Chen Liang]

> Simplify the layout access var handles to be direct in some common cases. Also made `VarHandle::isAccessModeSupported` report if an access mode is supported for a VH.
> 
> Reduces the instructions to execute this code in a simple main by 47%:
> 
> long[] arr = new long[8];
> var ms = MemorySegment.ofArray(arr);
> ms.setAtIndex(ValueLayout.JAVA_BYTE, 12, (byte) 3);
> 
> 
> Main overheads in FFM are identified to be:
> 1. Eager initialization of direct MethodHandle; can be CDS archived
> 2. MH combinator forms via LambdaFormEditor, not cached right now and always have large overhead
> 
> Still need other measures to deal with common user patterns of `MethodHandles.insertCoordinates(vh, 1, 0L)` which currently is still very slow.
> 
> Tests: 2 unrelated failures on tier 1-3

Chen Liang has updated the pull request incrementally with one additional commit since the last revision:

  Use "variable offset", remove extra makefile comments, comment fixes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23720/files
  - new: https://git.openjdk.org/jdk/pull/23720/files/e5839fb8..b995a268

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23720&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23720&range=04-05

  Stats: 31 lines in 6 files changed: 4 ins; 13 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/23720.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23720/head:pull/23720

PR: https://git.openjdk.org/jdk/pull/23720