RFR: 8350075: Performance difference between SegmentAllocator methods

[Per Minborg]

This PR proposes to add `@ForceInline` to the `default` methods in `SegmentAllocator` that do not already have it.

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Commit messages:
 - Add @ForceInline to default methods

Changes: https://git.openjdk.org/jdk/pull/23628/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23628&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350075
  Stats: 11 lines in 1 file changed: 11 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/23628.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23628/head:pull/23628

PR: https://git.openjdk.org/jdk/pull/23628