RFR: 8320645: DocLint should use javax.lang.model to detect default constructors

[Pavel Rappo]

jdk.javadoc.internal.doclint.Checker should favour the official javax.lang.model.util.Elements.getOrigin API over implementation-specific source tree positioning, to detect the default constructor.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/16790/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16790&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320645
  Stats: 8 lines in 1 file changed: 0 ins; 6 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16790.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16790/head:pull/16790

PR: https://git.openjdk.org/jdk/pull/16790