CASSANDRA-16939: Only remove shutdown hook for fatal heap OOMs

[Shanzita]

Description:
CASSANDRA-16939: Only remove shutdown hook for fatal heap
OOMs

Previously, StorageService.removeShutdownHook() was
called unconditionally
for all OutOfMemoryErrors in
JVMStabilityInspector.inspectThrowable().
This removed the drain shutdown hook even for non-fatal
OOMs like
"Direct buffer memory" or "unable to create new native
thread", preventing
graceful shutdown afterward even though the JVM was
otherwise healthy.

The fix guards removeShutdownHook() with a new
isHeapSpaceOom() method
that reuses the existing FORCE_HEAP_OOM_IGNORE_SET to
only remove the hook
for fatal heap OOMs ("Java heap space", "GC Overhead limit
exceeded").

Changes:

• JVMStabilityInspector.java: Guard
  removeShutdownHook() with isHeapSpaceOom() check
• JVMStabilityInspectorTest.java: Added tests verifying
  shutdown hook is preserved
  for non-fatal OOMs and removed for fatal OOMs

Tests:

• All existing tests pass (8/8, 0 failures)
• Checkstyle clean (0 violations)

patch by Shanizta Siddiqua; reviewed by for
CASSANDRA-16939