[code-reflection] Integrated: Only allow allocation via accelerator, and simplify schema binding

[Gary Frost]

We now restrict allocations of iface mappings to accelerators.  

Simplified the code for mapping schemas.  Some code in Schema should have  been in BoundSchema.

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Commit messages:
 - Only allow allocation via accelerator, and simplify schema binding

Changes: https://git.openjdk.org/babylon/pull/189/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=189&range=00
  Stats: 263 lines in 27 files changed: 77 ins; 117 del; 69 mod
  Patch: https://git.openjdk.org/babylon/pull/189.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/189/head:pull/189

PR: https://git.openjdk.org/babylon/pull/189