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

Start in BaseVariableWidthViewVector and inspect the out-of-line view handling in getData, getDataPointer, hashCode, copyFromNotNull, and splitAndTransferViewBufferAndDataBuffer. Compare the linked pull request, then verify that corrupt buffer indexes and offset/length ranges no longer permit out-of-bounds reads, including with unsafe memory access enabled.

Written by the indexing model from the issue text.