Problem:
In LSP configs, the function form of `cmd()` cannot easily get the
resolved root dir (workspace). One of the main use-cases of a dynamic
`cmd()` is to be able to start a new server whose binary may be located
*in the workspace* ([example](https://github.com/neovim/nvim-lspconfig/pull/3912)).
Compare `reuse_client()`, which also receives the resolved config.
Solution:
Pass the resolved config to `cmd()`.
Co-authored-by: Justin M. Keyes <justinkz@gmail.com>
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