[Java] Reject negative FieldNode length during deserialization #1421

Describe the bug

ArrowFieldNode accepts a negative length without validation. The IPC
(MessageSerializer.deserializeRecordBatch), JSON (JsonFileReader), and C Data
(ArrayImporter) deserialization paths all build ArrowFieldNode instances directly
from externally supplied metadata, so a malformed or hostile input can set a negative
node length.

A negative length is never valid, but today it propagates into buffer-size math in
BitVectorHelper.loadValidityBuffer (getValidityBufferSizeFromCount performs an
unsigned shift, turning a small negative into a ~512 MB allocation) and into
ArrowBuf.setOne / setZero with a negative byte count. With bounds checking enabled
this surfaces as an exception after a large buffer has already been allocated and the
vector's prior validity buffer released; with bounds checking disabled
(arrow.enable_unsafe_memory_access=true) the negative length reaches
Unsafe.setMemory and is reinterpreted as a huge unsigned length.

Expected behavior

Field node length is validated at the point of construction and a negative value is
rejected with a clear IllegalArgumentException before any buffer is sized or written.

Component(s)

Java