LazyVim has no Swift extra, so configure the pieces swift.org's Neovim
guide uses: the Treesitter swift parser and sourcekit-lsp from the
installed toolchain rather than Mason. lspconfig also assigns
sourcekit C, C++ and Objective-C, which would put a second server
beside clangd on those files, so limit it to Swift.
Format on save with conform's swift formatter, which runs the
toolchain's `swift format`; the standalone swift-format binary isn't
on PATH.
