RFR: 8315534: Incorrect warnings about implicit annotation processing

[Jan Lahoda]

When the API client sets annotation processors using `CompilationTask.setProcessors` and then uses `JavacTask` to drive the compiler using the `analyze()` method, the `compiler.note.implicit.annotation.processing` note is printed even though the annotation processing is explicit.

This patch is attempting to solve that by marking all processing with explicit processors as explicit.

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Commit messages:
 - 8315534: Incorrect warnings about implicit annotation processing

Changes: https://git.openjdk.org/jdk/pull/15540/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15540&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315534
  Stats: 102 lines in 2 files changed: 95 ins; 2 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/15540.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15540/head:pull/15540

PR: https://git.openjdk.org/jdk/pull/15540