RFR: JDK-8293177: Verify version numbers in legal files

[Hannes Wallnöfer]

Please review the addition of a new JavaDoc test to check the version of 3rd party libraries in legal files against the versions of actual library code. The skeleton for this test (mostly looking up files in the source tree) was taken from `CheckManPageOptions.java`. The test uses a regular expression to extract the name and version of 3rd party libraries in the `share/legal` directory and then matches these strings against the contents of the actual library files. 

The 3rd party libraries currently in use by JavaDoc are jQuery and jQuery-UI so the test infrastructure has some bits that facilitate JavaScript code such as support for both minified and unprocessed files, but it should work equally well for Java and other code.

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

Commit messages:
 - JDK-8293177: Verify version numbers in legal files

Changes: https://git.openjdk.org/jdk/pull/11211/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11211&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293177
  Stats: 149 lines in 1 file changed: 149 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11211.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11211/head:pull/11211

PR: https://git.openjdk.org/jdk/pull/11211