Fix Neovim documentation

[veigaribo]

Neovim 0.11 introduced the vim.lsp.config function for configuring LSP clients¹, and so the nvim-lspconfig became just a repository for LSP configuration, deprecating everything else². I thus updated the Neovim examples to invoke vim.lsp.config instead of the deprecated require'lspconfig'.….setup{}. I also removed references from lspconfig since it's technically not required anymore (or are we assuming the user does not know how to configure LSP in general?) and capitalized "neovim" to "Neovim" since that's how it's referred to in https://neovim.io/.

I also changed the cargo.allFeatures = true to cargo.features = "all" since that is also the new way of doing it³⁴. This change could probably be applied to the other examples as well.

1. https://neovim.io/doc/user/news-0.11.html
2. https://github.com/neovim/nvim-lspconfig?tab=readme-ov-file#important-%EF%B8%8F
3. Config revamp rust-lang/rust-analyzer#12010
4. https://rust-analyzer.github.io/book/configuration.html#cargo.features

[benwis]

Tricky! I appreciate the PR and the links. Things have certainly changed some in neovim