RFR: 8320234: Merge doclint.Env.AccessKind with tool.AccessKind

[Pavel Rappo]

Back when DocLint lived in jdk.compiler, neither jdk.javadoc had access to DocLint, nor DocLint had access to jdk.javadoc. Since DocLint moved to jdk.javadoc, some redundancy can be eliminated and functionality shared; AccessKind is one such functionality.

There's more that could be done here. For example, jdk.javadoc.internal.doclint.Messages.Options can be simplified more. However, it's a separate issue.

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Commit messages:
 - Aggressively simplify code
 - Clean up more
 - Clean up
 - Rename AccessKind to reflect its level semantics
 - Merge two AccessKind into tool.AccessKind
 - Move DocLint-specific method from Env.AccessKind

Changes: https://git.openjdk.org/jdk/pull/16714/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16714&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320234
  Stats: 304 lines in 8 files changed: 84 ins; 134 del; 86 mod
  Patch: https://git.openjdk.org/jdk/pull/16714.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16714/head:pull/16714

PR: https://git.openjdk.org/jdk/pull/16714