[jdk17u-dev] RFR: 8287007: [cgroups] Consistently use stringStream throughout parsing code

[Goetz Lindenmaier]

I backport this for parity with 17.0.8-oracle.

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Commit messages:
 - Backport e0baf012b111e422ddf39a577b1b4af2599fd00d

Changes: https://git.openjdk.org/jdk17u-dev/pull/1251/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1251&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8287007
  Stats: 262 lines in 5 files changed: 228 ins; 19 del; 15 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1251.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1251/head:pull/1251

PR: https://git.openjdk.org/jdk17u-dev/pull/1251