RFR: JDK-8272853: improve `JavadocTester.runTests`

[Jonathan Gibbons]

Please review a medium simple test-only fix to improve the `JavadocTester` `runTests` methods.

Currently, there are two overloads: one to invoke no-args test methods, and another to invoke test methods with args, such as a method-specific `Path`.  This latter one is slightly inconvenient to use, since it requires the boilerplate use of a function to create the arguments.

The first overload is updated in a backwards compatible way, to examine the parameters of methods annotated with `@Test`, and to recognize common patterns: namely no-args methods and `(Path)` methods, without the need for any additional function.  The second overload is retained by backwards compatibility, until if and when we decide it is no longer required.

In addition, two new overloads are added, similar to the first two, but with the addition of an extra parameter to decide which methods should be invoked. This is primarily a debugging aid.  Using these overloads, it is easy to specify, on the command line used to run the test, the methods to be executed.

A new test is added to test the new functionality.

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Commit messages:
 - JDK-8272853: improve `JavadocTester.runTests`

Changes: https://git.openjdk.java.net/jdk/pull/6983/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6983&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272853
  Stats: 370 lines in 2 files changed: 359 ins; 6 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6983.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6983/head:pull/6983

PR: https://git.openjdk.java.net/jdk/pull/6983