[code-reflection] Integrated: Moved BoundSchema to its own interface

[Gary Frost]

BoundSchema was inner class of Schema. Moved it out. 
Created BackendAdaptor for testing SSA Ptr work. 
Starting to move use of BoundSchema into HatPtr types.

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Commit messages:
 - Moved BoundSchema to its own interface

Changes: https://git.openjdk.org/babylon/pull/177/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=177&range=00
  Stats: 851 lines in 26 files changed: 299 ins; 437 del; 115 mod
  Patch: https://git.openjdk.org/babylon/pull/177.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/177/head:pull/177

PR: https://git.openjdk.org/babylon/pull/177