RFR: 8303891: Zip64SizeTest could use a sparse file [v2]

[Eirik Bjorsnos]

> This PR suggests we use a sparse file when the Zip64SizeTest writes a ZIP file with a 5GB entry.
> 
> The size requirement of this test is known to cause problems in some builds, see [JDK-8259866](https://bugs.openjdk.org/browse/JDK-8259866)
> 
> Using a sparse file reduces the disk space requirements of running the test from 5GB to 12K and also reduces the runtime from ~35 seconds to ~3 seconds on my Macbook Pro.

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

  Make test method public

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12948/files
  - new: https://git.openjdk.org/jdk/pull/12948/files/7f4643a1..d3a8d785

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12948&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12948&range=00-01

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12948.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12948/head:pull/12948

PR: https://git.openjdk.org/jdk/pull/12948