[C++][Acero] Buffers returned by filter node use the default memory pool

### Describe the bug, including details regarding any error messages, version, and platform.

The buffers returned by the filter node use the default memory pool instead of the memory pool from the exec context. This is because the filter node does not pass the exec context to the filter function. I already found the fix and will submit a pull request.

### Component(s)

C++