RFR: 8321114: Rename "Unnamed Classes" to "Implicitly Declared Classes" better

[Pavel Rappo]

Please review this PR to correctly rename "Unnamed Class" to "Implicitly Declared Class", not "Implicit Class".

Renaming is fixed where it affects documentation or the end-user. Renaming is not fixed where it only affects code: it's perfectly okay to derive an internal element name from "Implicit Class" rather than "Implicitly Declared Class", for brevity.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/16904/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16904&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321114
  Stats: 18 lines in 8 files changed: 0 ins; 0 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/16904.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16904/head:pull/16904

PR: https://git.openjdk.org/jdk/pull/16904