[code-reflection] RFR: Rename TypeVarRef to TypeVariableType

[Paul Sandoz]

Rename `TypeVarRef` to `TypeVariableType`

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Commit messages:
 - Rename TypeVarRef to TypeVariableType

Changes: https://git.openjdk.org/babylon/pull/417/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=417&range=00
  Stats: 19 lines in 7 files changed: 0 ins; 4 del; 15 mod
  Patch: https://git.openjdk.org/babylon/pull/417.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/417/head:pull/417

PR: https://git.openjdk.org/babylon/pull/417