Removes usage of several deprecated API functions, and changes all uses
of `vim.loop` to `vim.uv`.
Now that 0.10 is released, several functions used here have been
deprecated and show warnings when they're first called.
I've updated:
- `lsp.get_active_clients()` -> `lsp.get_clients()`
- `api.nvim_buf_set_option` -> `api.nvim_set_option_value` with
buf-local scope
- `api.nvim_win_set_option` -> `api.nvim_set_option_value` with
window-local scope
- `vim.tbl_flatten` -> `vim.iter(t):flatten():totable()`
- `vim.loop.*` -> `vim.uv.*`
- `vim.islist or vim.tbl_islist` -> `vim.islist`
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Co-authored-by: Folke Lemaitre <folke.lemaitre@gmail.com>