The first argument which is non-nil is returned. This is useful when
using nested default values (e.g. in the EditorConfig plugin).
Before:
local enable = vim.F.if_nil(vim.b.editorconfig, vim.F.if_nil(vim.g.editorconfig, true))
After:
local enable = vim.F.if_nil(vim.b.editorconfig, vim.g.editorconfig, true)
Rather than only check `editorconfig_enable` when the plugin is loaded,
check it each time the autocommand fires, so that users may enable or
disable it dynamically.
Also check for a buffer local version of the variable, so that
editorconfig can be enabled or disabled per-buffer.
