[code-reflection] RFR: Compare code elements and values.

[Paul Sandoz]

Compare code elements by their by comparing their pre-order traversal positions in the code model.

Comparing values compares their declaring code elements (prior code was not correct, in general).

-------------

Commit messages:
 - Doc update.
 - Compare code elements and values.

Changes: https://git.openjdk.org/babylon/pull/850/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=850&range=00
  Stats: 267 lines in 3 files changed: 215 ins; 32 del; 20 mod
  Patch: https://git.openjdk.org/babylon/pull/850.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/850/head:pull/850

PR: https://git.openjdk.org/babylon/pull/850