RFR: 8355681: G1HeapRegionManager::find_contiguous_allow_expand ignores free regions when checking regions available for allocation

[Ivan Walulya]

Hi,

Please review this change to account for free regions when checking if we have enough regions to satisfy an allocation request. Currently, we have that a `_hrm.expand_and_allocate_humongous` call fails where an `expand_and_allocate` call succeeds for the same allocation request. 

Testing: Tier 1-3

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Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/24915/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24915&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8355681
  Stats: 13 lines in 2 files changed: 5 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/24915.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24915/head:pull/24915

PR: https://git.openjdk.org/jdk/pull/24915