[code-reflection] Integrated: ArgBuffer now using schema

[Gary Frost]

Continuing the migration of buffers from manual layout to schema. 

Specifically ArgBuffer, used to convery args from java to native code.

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Commit messages:
 - ArgBuffer now using schema

Changes: https://git.openjdk.org/babylon/pull/173/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=173&range=00
  Stats: 100 lines in 3 files changed: 37 ins; 19 del; 44 mod
  Patch: https://git.openjdk.org/babylon/pull/173.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/173/head:pull/173

PR: https://git.openjdk.org/babylon/pull/173