This decreases the number of samples significantly, leading to a
notable performance increase with only a very slight loss in
visual quality.
This also tweaks the default SSAO settings to use 3×3 blurring,
which makes noise patterns much less visible.
As of clang-format 6.0.1, putting the `/* clang-format off */` hint
around our "invalid" `[vertex]` and `[shader]` statements isn't enough
to prevent a bogus indent of the next comments and first valid statement,
so we need to enclose that first valid statement in the unformatted chunk.
