perfetto: Add a .clang-format for the directory.

perfetto: Add a .clang-format for the directory.

I was frustrated trying to write code and not be able to just mash ^K^F to
format what I'd written.  This .clang-format is just cargo-cult of turnip
with a few tweaks to reduce the diff to the current directory contents.
The remaining deltas in the reformat look decent to me, and mostly bring
things closer to mesa-vague-consensus style.

Reviewed-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22157>