LUCENE-10128: avoid costly reflection in SparseFixedBitSet ctor

Seems that VectorFormat merge creates A LOT of these bitsets. We don't
need to do any fancy reflection here via shallowSizeOf(Object), when we
can call sizeOf(long[]) which is fast.

We may want to revisit this RAMUsageEstimator api in the future to
prevent traps like this.

lucene/core/src/java/org/apache/lucene/util/SparseFixedBitSet.java

@@ -69,7 +69,7 @@ public class SparseFixedBitSet extends BitSet {
     bits = new long[blockCount][];
     ramBytesUsed =
         BASE_RAM_BYTES_USED
-            + RamUsageEstimator.shallowSizeOf(indices)
+            + RamUsageEstimator.sizeOf(indices)
             + RamUsageEstimator.shallowSizeOf(bits);
   }