RFR: 8303920: Avoid calling out to python in DataDescriptorSignatureMissing test [v6]

[Eirik Bjorsnos]

> Please review this PR which brings  the DataDescriptorSignatureMissing test back to life.
> 
> This test currently calls out to Python to create a test vector ZIP with a Data Descriptor without the recommended but optional signature. The Python dependency has turned out to be very brittle, so the test is currently marked with `@ignore` 
> 
> The PR replaces Python callouts with directly creating the test vector ZIP in the test itself. We can then remove the `@ignore`tag and run this useful test automatically.

Eirik Bjorsnos has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains eight additional commits since the last revision:

 - Merge branch 'master' into signature-less-data-descriptor
 - Add assertNotNulls to catch unexpectedly missing entries
 - Revert change to Google copyright line, add an Oracle copyright line instead.
 - Use "Signatureless" consistently
 - Remove reference to python in the @summary of DataDescriptorSignatureMissing
 - Update copyright years
 - Add method comments
 - Instead of calling out to python, create a ZIP file and remove the data descriptor signature.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12959/files
  - new: https://git.openjdk.org/jdk/pull/12959/files/85eab4a3..0fb30670

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12959&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12959&range=04-05

  Stats: 8132 lines in 183 files changed: 1014 ins; 1302 del; 5816 mod
  Patch: https://git.openjdk.org/jdk/pull/12959.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12959/head:pull/12959

PR: https://git.openjdk.org/jdk/pull/12959