Add `.swift-format` to the repo and format the repo with `swift-format`.
This commit does not add any automation to enforce formatting of sourcekit-lsp in CI. The goal of this commit is to get the majority of source changes out of the way so that the diff of actually enforcing formatting will have fewer changes or conflicts.
Since Musl is sufficiently different from Glibc (see https://wiki.musl-libc.org/functional-differences-from-glibc.html), it requires a different import, which now should be applied to files that have `import Glibc` in them.
Musl is a low footprint libc that's used in Linux distributions such as Alpine Linux, which allows producing fairly small container images. Additionally, unlike Glibc, musl allows full static linking, meaning apps can be easily distributed to an arbitrary Linux distribution that may have a version of Glibc incompatible with the one that Swift is usually built with or no Glibc installed at all.
