RFR: JDK-8323628: Update license on "pass-through" files

[Jonathan Gibbons]

Please review an update to change the license used on those files that get written by `javadoc` into any generated API doc bundles. The license is changed to the Universal Permissive License in all situations.

A new test is added to verify the license is found on all appropriate files in the `resource-files` and `script-files` directories. One test, to detect and check CSS classes, was modified to ignore a false positive in the new comment in the stylesheet.css file.

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Commit messages:
 - JDK-8323628: Update license on "pass-through" files

Changes: https://git.openjdk.org/jdk/pull/17411/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17411&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323628
  Stats: 251 lines in 9 files changed: 129 ins; 108 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/17411.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17411/head:pull/17411

PR: https://git.openjdk.org/jdk/pull/17411