[3.10] gh-93738: Documentation C syntax (:c:type:`FILE` -> :c:expr:`FILE`) (GH-97769) (#97872)

:c:type:`FILE` -> :c:expr:`FILE`
(cherry picked from commit 192d401ba53224020f5f9ca6e1ff2c9f89511ac4)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>