[code-reflection] RFR: Structured type definition [v4]

[Paul Sandoz]

> Replace the currently implementation of `TypeDefinition` with a more general tree structure, which is the boundary between the runtime and serialized form.
> 
> This should help when/if we devise a richer modeling of Java types

Paul Sandoz has updated the pull request incrementally with one additional commit since the last revision:

  Reabsract TypeElement toString, equals, and hashCode.

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Changes:
  - all: https://git.openjdk.org/babylon/pull/23/files
  - new: https://git.openjdk.org/babylon/pull/23/files/88982b77..d1e574fa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=23&range=03
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=23&range=02-03

  Stats: 16 lines in 2 files changed: 12 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/babylon/pull/23.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/23/head:pull/23

PR: https://git.openjdk.org/babylon/pull/23