RFR: 8294437: java/nio/channels/FileChannel tests slow on Windows [v6]

[Daniel Jeliński]

> Please review this test-only change that improves the execution speed of a few FileChannel tests:
> - Transfer2GPlus, Transfer4GBFile, and TransferTo6GBFile were modified to use sparse files. Their speed is now consistent across platforms, provided that the platform / filesystem supports sparse files.
> - LargeMapTest was rewritten to use sparse files, and to more precisely target the issue it was written to detect. In my tests it still crashed with EXCEPTION_ACCESS_VIOLATION when JDK-8286637 was reverted.
> - MapTest: repetition was removed from `testForce` method; I'm not sure what issues it was supposed to catch, but at far as I can tell, it was only triggering timeouts, see [JDK-8289526](https://bugs.openjdk.org/browse/JDK-8289526), [JDK-8224480](https://bugs.openjdk.org/browse/JDK-8224480)

Daniel Jeliński has updated the pull request incrementally with one additional commit since the last revision:

  Fix typo

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10464/files
  - new: https://git.openjdk.org/jdk/pull/10464/files/0f22fb54..148ea2cc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10464&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10464&range=04-05

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10464.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10464/head:pull/10464

PR: https://git.openjdk.org/jdk/pull/10464