Move IPC format reader/writer and FlatBuffers bindings into a separate module.

### Describe the enhancement requested

The Arrow IPC format code is currently part of the core Arrow target, however it is not essential to core functionality.

**Proposed change:**
Move the IPC reader/writer code and FlatBuffers schema bindings into a separate Swift module (e.g. ArrowIPC) in line with how other Arrow implementations organize these components.
Add the new module to the ArrowFlight dependencies.

**Benefits:**
Simplifies Arrow core.
FlatBuffers becomes an optional dependency.
Aligns with how [arrow-rs](https://github.com/apache/arrow-rs) separates IPC in the arrow-ipc crate.
Simplifies integration for projects that don’t use IPC or Flight.

Start by locating the Arrow IPC reader/writer code, FlatBuffers schema bindings, and the ArrowFlight dependency definition. Done means IPC and its bindings are in a separate Swift module, ArrowFlight depends on that module, and core Arrow no longer requires the optional FlatBuffers dependency.

Written by the indexing model from the issue text.