We don't actually support snippets in core in the way that users would
truly expect. So, by default, we will not say that builtin-lsp has
`snippetSupport`.
To re-enable, users can do the following:
First, get a capabilities dictionary with
`local capabilities = vim.lsp.protocol.make_client_capabilities()`
Then override
`capabilities.textDocument.completion.completionItem.snippetSupport = true`
and then pass those capabilties to the setup function.
```
nvim_lsp.server_name.setup {
...,
capabilities = capabilities,
...,
}
```
See https://github.com/neovim/neovim/issues/12795
98024853f4
