[crac] RFR: Linux file system watcher support [v2]

[joeylee]

> inotify monitors changes on filesystem, this support automatic restore for LinuxFileWatcher.
> 
> FileWatcherAfterRestoreTest verifies watcher service works after restore.
> FileWatcherTest verifies automatic closing inotiify fd
> 
> The watcher keys are still managed by user, so exception will be thrown if no watcher keys are leaked, as in FileWatcherWithOpenKeysTest

joeylee has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  Linux file system watcher support

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Changes:
  - all: https://git.openjdk.org/crac/pull/72/files
  - new: https://git.openjdk.org/crac/pull/72/files/20f4bee1..36dfd224

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=72&range=01
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=72&range=00-01

  Stats: 73 lines in 3 files changed: 8 ins; 54 del; 11 mod
  Patch: https://git.openjdk.org/crac/pull/72.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/72/head:pull/72

PR: https://git.openjdk.org/crac/pull/72