RFR: JDK-8309594 Cleanup naming in JavacParser related to unnamed classes

[Jim Laskey]

Some residual names (anon) from early unnamed classes work.

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Commit messages:
 - Rename anon to unnamed

Changes: https://git.openjdk.org/jdk/pull/14351/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14351&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309594
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/14351.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14351/head:pull/14351

PR: https://git.openjdk.org/jdk/pull/14351