GH-2142, GH-3751: Backport proto-bytes fixes to 1.18.x (#3750, #3752) - #3844

…ache#3750)

### Rationale for this change

Protobuf allows empty message definitions, but Parquet forbids empty groups. Converting a message
that merely *contains* a field of an empty message type produces a schema with an empty group,
which writer construction rejects with `InvalidSchemaException: Cannot write a schema with an
empty group`. Such fields appear in real-world schemas (deprecated stubs, marker/placeholder
messages), and a single one makes the whole message type unwritable.

### What changes are included in this PR?

`ProtoSchemaConverter.addMessageField` terminates a field whose message type has no fields as a
`BINARY` column holding the serialized message — the same mechanism PARQUET-1711 uses for
recursion beyond `maxRecursion`. Since an empty message serializes to zero bytes, the column is
cheap, and field **presence** still round-trips (null = unset vs empty bytes = set):

- singular field → `optional binary stub` (or `required`, per the field);
- repeated field, parquet-specs mode → LIST-wrapped binary via the existing
  `addRepeatedPrimitive`, so element cardinality survives;
- repeated field, old style → `repeated binary`;
- map value type → `optional binary value` inside the `key_value` group (keys stay typed).

`ProtoWriteSupport.createMessageWriter`'s existing truncated-field check (primitive BINARY where a
message field was declared → `BinaryWriter`) is generalized to look through the LIST/MAP wrapper
(`getGroupType` → `getContentType`), so the writer tree lines up with these schemas.

A message that is empty at the **root** is still rejected — there is no parent field to hold the
bytes, and a Parquet file with zero columns is not representable.

**Read side** (second commit, after review): `ProtoMessageConverter` used to cast every message
field's Parquet type to a group, so a message field stored as `BINARY` failed with a
`ClassCastException` while the converter tree was built — which also means files with
PARQUET-1711 recursion truncation have been unreadable by `ProtoParquetReader` since 1.13.0 (apache#995
shipped with an explicit "TODO: ReadSupport"). A new `ProtoBinaryMessageConverter` parses the
bytes back through `parentBuilder.newBuilderForField(field)` and hands the message to the existing
parent container, so singular fields, LIST elements, old-style repeated fields and map values all
round-trip without touching `ListConverter`/`MapConverter`. Parse failures surface as
`ParquetDecodingException`.

### Are these changes tested?

Yes. New `ProtoEmptyMessageTest` (new test messages `Stub`/`StubBox` in `Trees.proto`) writes
through the real write path (`ProtoParquetWriter` → `MessageColumnIO`, both specs-compliant and
old style) and reads back with `GroupReadSupport` and with `ProtoParquetReader`:

- singular / repeated / map-value empty-message fields round-trip with correct cardinality and
  zero-byte values;
- presence round-trips (set empty message vs unset field);
- `ProtoParquetReader` reads the written messages back equal to the originals (specs-compliant and
  old style), and the same read path round-trips a `BinaryTree` truncated at `maxRecursion`;
- an empty root message still fails with `InvalidSchemaException` ("Cannot write a schema with an
  empty group").

`ProtoSchemaConverterTest.testEmptyMessageFields` pins the converted schema. The full
parquet-protobuf suite passes (117 tests).

### Are there any user-facing changes?

Message types that previously could not be written to Parquet at all now can; fields of empty
message types appear as (possibly LIST/MAP-wrapped) `binary` columns and read back into the
original messages with `ProtoParquetReader`. Files with `maxRecursion` truncation, previously
unreadable by `ProtoParquetReader`, now read back as well. No change for schemas that were
previously writable. Error behavior for an empty root message is unchanged.

Closes apache#2142