Add a Stylo bindings sanity test

This commit adds a sanity test that we can generate bindings for Stylo without
any errors. I tried to make this a `#[bench]` but each iteration takes 36
seconds on my machine, which made the `#[bench]` take *way* too long. Instead,
there is a commented out `panic!` that can be uncommented to get a log of how
long it took.

Author: fitzgen

.gitattributes

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+tests/stylo.hpp -diff