RFR: 8303972: TestLocOffsetFromZip64EF could use a sparse file [v2]

[Eirik Bjorsnos]

> Please review this PR which brings the currenly problem-listed test TestLocOffsetFromZip64EF back to life.
> 
> By using a sparse ZIP file instead of calling out to the `zip` command line, we can speed up the test (from 50s to 3s on my Macbook Pro), save 4GB disk space during builds and remove a dependency on the `zip` command in OS/distros.
> 
> To get an idea on how the new test performs on file systems which do not support sparse files, I also ran the using a disk image in MacOS with a non-spase file system. The test completed in 14 seconds.
> 
> Seee [JDK-8301183](https://bugs.openjdk.org/browse/JDK-8301183) for details on the problem-listing.

Eirik Bjorsnos has updated the pull request incrementally with one additional commit since the last revision:

  Instead of making a big file to force Zip64, make a small file with a Zip64-formatted CEN header.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12979/files
  - new: https://git.openjdk.org/jdk/pull/12979/files/ee8adc0c..2efd7275

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12979&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12979&range=00-01

  Stats: 107 lines in 1 file changed: 49 ins; 23 del; 35 mod
  Patch: https://git.openjdk.org/jdk/pull/12979.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12979/head:pull/12979

PR: https://git.openjdk.org/jdk/pull/12979