Revert "plugins/lsp: use vim.lsp native API"

[MattSturgeon]

This reverts commit 78f6ff0 from #3204

See discussion: #3204 (comment)

I think we may have to revert this for a while, as not all nvim-lspconfig configs are updated to work with the new API.

Our users are running into issues like:

• [BUG] Omisharp LSP fails to attach #3217 (comment)
• [BUG] nvim-lspconfig default configuration missing for eslint #3224

Which may not be fully resolvable until neovim/nvim-lspconfig#3705 is complete and propagated to nixpkgs.

Hopefully we will be able to un-revert soon, once nvim-lspconfig has updated the remaining configs.

Users can test by overriding their flake input:

nix flake lock --override-input nixvim 'github:nix-community/nixvim?ref=pull/3233/merge'

Then they should try using their config, e.g. with nix run .#nvim. In particular, you should check :checkhealth vim.lsp has your LSPs configured correctly.

Fixes #3217
Fixes #3224

[mergify]

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