[code-reflection] Integrated: Hat mark buffers

[Gary Frost]

Ungoing changes. As we add ability to avoid unnecessary buffer copies via buffer marking. 

Moved info previously in the ArgSled (from Java to FFI code) into the buffers themselves. 

At present we still copy all in and out of kernel dispatches.

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Commit messages:
 - Ungoing transition to avoiding copies via buffer marking
 - Added Buffer.Tail for accessing mark bits.
 - Removed buffer marking from sled, now the buffers themselves are marked
 - Add 256 bit marker tail to each segment buffer

Changes: https://git.openjdk.org/babylon/pull/317/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=317&range=00
  Stats: 596 lines in 30 files changed: 224 ins; 282 del; 90 mod
  Patch: https://git.openjdk.org/babylon/pull/317.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/317/head:pull/317

PR: https://git.openjdk.org/babylon/pull/317