[code-reflection] RFR: Separate TypeElement from Type.

[Paul Sandoz]

`TritonType` currently extends from `TypeElement` and `Type` to allow for the convenient composition of a code model type (symbolical description of a type) and a runtime type. This is confusing, and is mixing layers. `TritonType` should only extended from `TypeElement` and same for any arguments of.

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Commit messages:
 - Separate TypeElement from Type.

Changes: https://git.openjdk.org/babylon/pull/29/files
 Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=29&range=00
  Stats: 305 lines in 16 files changed: 10 ins; 55 del; 240 mod
  Patch: https://git.openjdk.org/babylon/pull/29.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/29/head:pull/29

PR: https://git.openjdk.org/babylon/pull/29