ByteBufferBackingArray should recognize hasArray() guards

[bc-lee]

Background:
In https://bugs.webrtc.org/42234355, I'm trying to remove @SuppressWarnings("ByteBufferBackingArray") and add proper ByteBuffer backing array checks.

The following code seems the correct pattern for safely accessing a ByteBuffer's backing array:

final int frameSize = 100;
final ByteBuffer buffer = ByteBuffer.allocateDirect(frameSize);
if (buffer.hasArray()) {
  buffer.array();
} else {
  final byte[] array = new byte[frameSize];
  buffer.get(array);
}

However, Error Prone's ByteBufferBackingArray checker incorrectly flags this as unsafe.

Current behavior:
Upon reviewing ByteBufferBackingArray.java, the checker currently only accepts:

• Calls to ByteBuffer.arrayOffset()
• Buffers created with ByteBuffer.wrap() or ByteBuffer.allocate()

This is insufficient for the recommended hasArray() guard pattern.

Expected behavior:
The checker should accept array() calls when properly guarded by conditional hasArray() checks.

Should NOT warn:

final ByteBuffer buffer = ByteBuffer.allocateDirect(100);
if (buffer.hasArray()) {
  buffer.array(); // Safe - guarded by hasArray()
}

Should warn:

final ByteBuffer buffer = ByteBuffer.allocateDirect(100);
buffer.hasArray(); // Just calling hasArray() without using the result
buffer.array();    // Unsafe - no conditional protection

Suggestion:
Enhance ByteBufferBackingArray to recognize when array() calls are control-flow guarded by hasArray() conditions, treating them as safe usage patterns.