Out-of-bounds read for corrupt view offsets in BaseVariableWidthViewVector

### Describe the bug

`ViewVarCharVector`/`ViewVarBinaryVector` store values longer than `INLINE_SIZE` (12 bytes) out of line, encoding a data-buffer index and an offset inline in the view buffer. When a vector is loaded from an IPC stream these fields come straight from the input.

`BaseVariableWidthViewVector` dereferences them verbatim in `getData`, `getDataPointer`, `hashCode`, `copyFromNotNull` and `splitAndTransferViewBufferAndDataBuffer`, e.g.

```java
dataBuffers.get(bufferIndex).getBytes(dataOffset, result, 0, dataLength);
```

Nothing checks that `bufferIndex` is in range or that `dataOffset + dataLength` fits inside the referenced data buffer. A crafted view whose offset/length points past the data buffer produces an out-of-bounds read: with the default bounds checking it throws `IndexOutOfBoundsException`, but with `arrow.enable_unsafe_memory_access=true` (commonly set in production) it reads arbitrary native heap into the returned value.

### Component(s)

Java

Beginne in BaseVariableWidthViewVector und untersuche die Out-of-line-View-Behandlung in getData, getDataPointer, hashCode, copyFromNotNull und splitAndTransferViewBufferAndDataBuffer. Vergleiche den verknüpften Pull Request und überprüfe anschließend, dass beschädigte Buffer-Indizes und Offset-/Length-Bereiche keine Lesezugriffe außerhalb der Grenzen mehr ermöglichen, auch wenn der unsafe memory access aktiviert ist.

Vom Indexierungsmodell aus dem Issue-Text verfasst.