arrow

GH-36120: [C#] Support schema metadata through the C API (#36122)

### What changes are included in this PR?

Import and export of field- and schema-level metadata via the C API.

### Are these changes tested?

Yes

* Closes: #36120

Authored-by: Curt Hagenlocher <curt@hagenlocher.org>
Signed-off-by: Will Jones <willjones127@gmail.com>