[jdk18u] RFR: 8281181: Do not use CPU Shares to compute active processor count

[Ioi Lam]

Please review this backport of [JDK-8281181](https://bugs.openjdk.java.net/browse/JDK-8281181) to jdk18u. Most changes were cleanly applied, except:

- The changes in related to the deprecation of UseContainerCpuShares and PreferContainerQuotaForCPUCount) have been dropped. That's because the deprecation happens in the JDK 19 release cycle, not in 18u.

You can compare with the JDK 19 version of the changes [here](https://github.com/openjdk/jdk/pull/7666/files).

Tested with tiers 1-5, including all container test tasks.

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Commit messages:
 - Backport e07fd395bdc314867886a621ec76cf74a5f76b89

Changes: https://git.openjdk.java.net/jdk18u/pull/79/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18u&pr=79&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281181
  Stats: 43 lines in 4 files changed: 28 ins; 0 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk18u/pull/79.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18u pull/79/head:pull/79

PR: https://git.openjdk.java.net/jdk18u/pull/79