RFR: 8324668: JDWP process management needs more efficient file descriptor handling [v4]

[Jaikiran Pai]

> Can I please get a review of this change which proposes to address https://bugs.openjdk.org/browse/JDK-8324668?
> 
> This change proposes to fix the issue in jdwp where when launching a child process (for the `launch=<cmd>` option), it iterates over an extremely large number of file descriptors to close each one of those. Details about the issue and the proposed fixed are added in a subsequent comment in this PR https://github.com/openjdk/jdk/pull/17588#issuecomment-1912256075. tier1, tier2 and tier3 testing is currently in progress with this change.

Jaikiran Pai has updated the pull request incrementally with three additional commits since the last revision:

 - add a log message to help debuggability
 - improve code comments
 - David's review - use standard isdigit instead of custom isAsciiDigit

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17588/files
  - new: https://git.openjdk.org/jdk/pull/17588/files/af2472d4..e4a8573b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17588&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17588&range=02-03

  Stats: 25 lines in 1 file changed: 4 ins; 6 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/17588.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17588/head:pull/17588

PR: https://git.openjdk.org/jdk/pull/17588