RFR: JDK-8286311: remove boilerplate from use of runTests

[Jonathan Gibbons]

Please review a test-only cleanup for JDK 21.

There are two mostly-automated (IDE) changes here:

1. Remove redundant boiler-plate arguments from calls to `JavadocTester.runTests()`.  The use of a function to derive and provide a method-specific directory because unnecessary with JDK-
2. Use `var` for the declaration of the `tester` variable found in the `main` method of most javadoc tests.

The changes were mostly done with IDEA _Replace in Files..._, with some manual fixup for some outlying cases found while checking the code.

-------------

Commit messages:
 - JDK-8286311: remove boilerplate from use of runTests

Changes: https://git.openjdk.org/jdk/pull/11746/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11746&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8286311
  Stats: 345 lines in 269 files changed: 0 ins; 0 del; 345 mod
  Patch: https://git.openjdk.org/jdk/pull/11746.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11746/head:pull/11746

PR: https://git.openjdk.org/jdk/pull/11746