Move the memstream code into common code. Other Rust code interfacing
with FILE pointers will find the memstream abstraction useful.
Most notably, pinning is actually enforced this time with PhantomPinned.
Add a .clang-format from a sibling dir (i.e.: compiler/nir) while we're
at it to keep things tidy.
Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30594>
