RFR: 8303891: Speed up Zip64SizeTest using a small ZIP64 file [v6]

[Eirik Bjørsnøs]

> Please review this PR which suggests we speed up the `Zip64SizeTest` using a small-sized ZIP64 ZIP file specifically created to reproduce the issue being tested.
> 
> The disk space requirement of this test is known to cause problems in some builds, see [JDK-8259866](https://bugs.openjdk.org/browse/JDK-8259866)
> 
> By using a sparse file, we reduce consumed disk space from 5GB to 266 bytes and also reduce the runtime from ~35 seconds to ~1 seconds on my Macbook Pro.
> 
> The PR also fixes the `@summary` tag, which seems to have been copied from an unrelated test.

Eirik Bjørsnøs has updated the pull request incrementally with two additional commits since the last revision:

 - Spell fix for "Contents"
 - Add comments to explain how we temporarily use the 'unknown' tag to prevent ZipEntry.setExtra0 from processing the extra field.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12948/files
  - new: https://git.openjdk.org/jdk/pull/12948/files/41b2ba5e..34333c98

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12948&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12948&range=04-05

  Stats: 27 lines in 1 file changed: 9 ins; 2 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/12948.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/12948/head:pull/12948

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