RFR: 8344079: Minor fixes and cleanups to compiler lint-related code [v3]

[Archie Cobbs]

> Please review these changes with some minor lint-related fixes and cleanups.
> 
> See [JDK-8344079](https://bugs.openjdk.org/browse/JDK-8344079) for a more detailed description.

Archie Cobbs has updated the pull request incrementally with one additional commit since the last revision:

  Fold LintSuppression methods back into existing Lint class.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/22056/files
  - new: https://git.openjdk.org/jdk/pull/22056/files/8b961d48..7cb7aa0c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22056&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22056&range=01-02

  Stats: 197 lines in 2 files changed: 65 ins; 127 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/22056.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22056/head:pull/22056

PR: https://git.openjdk.org/jdk/pull/22056