arrow

GH-36036: [C++][Python][Parquet] Implement Float16 logical type (#36073)



### Rationale for this change

There is currently an active proposal to support half-float types in Parquet. For more details/discussion, see the links in this PR's accompanying issue.

### What changes are included in this PR?

This PR implements basic support for a `Float16LogicalType` in accordance with the proposed spec. More specifically, this includes:

- Changes to `parquet.thrift` and regenerated `parqet_types` files
- Basic `LogicalType` class definition, method impls, and enums
- Support for specialized comparisons and column statistics

In the interest of scope, this PR does not currently deal with arrow integration and byte split encoding - although we will want both of these features resolved before the proposal is approved.

### Are these changes tested?

Yes (tests are included)

### Are there any user-facing changes?

Yes

* Closes: #36036

Lead-authored-by: benibus <bpharks@gmx.com>
Co-authored-by: Ben Harkins <60872452+benibus@users.noreply.github.com>
Co-authored-by: Antoine Pitrou <pitrou@free.fr>
Signed-off-by: Antoine Pitrou <antoine@python.org>