RFR: JDK-8319046: Execute tests in source/class-file order in JavadocTester

[Jonathan Gibbons]

Please review an update to `JavadocTester` to execute the default set of test methods in source-file order.

The order can be changed by overriding the new `getMethodComparator` method.

Code is provided, but commented out, to determine the methods in class-file order, for use when the new classfile library moves out of preview.  (Using it before then would require updating all the jtreg test descriptions for all tests that use `JavadocTester`.)

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Commit messages:
 - JDK-8319046: Execute tests in source/class-file order in JavadocTester

Changes: https://git.openjdk.org/jdk/pull/16438/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16438&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319046
  Stats: 69 lines in 1 file changed: 62 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/16438.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16438/head:pull/16438

PR: https://git.openjdk.org/jdk/pull/16438