[code-reflection] RFR: Updates to CodeItem and subtypes.

[Paul Sandoz]

Documentation and terminology updates to `CodeItem` and subtypes.

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Commit messages:
 - Updates to CodeItem and subtypes.

Changes: https://git.openjdk.org/babylon/pull/881/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=881&range=00
  Stats: 367 lines in 9 files changed: 165 ins; 116 del; 86 mod
  Patch: https://git.openjdk.org/babylon/pull/881.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/881/head:pull/881

PR: https://git.openjdk.org/babylon/pull/881