[jdk16] RFR: JDK-8258443: doclint should be service-loaded with system class loader

[Jonathan Gibbons]

Trivial fix to use the system class loader when loading doclint for javac

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Commit messages:
 - JDK-8258443: doclint should be service-loaded with system class loader

Changes: https://git.openjdk.java.net/jdk16/pull/54/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16&pr=54&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258443
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk16/pull/54.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16 pull/54/head:pull/54

PR: https://git.openjdk.java.net/jdk16/pull/54