feat(editorconfig): allow editorconfig to be toggled dynamically

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.

runtime/plugin/editorconfig.lua

@@ -1,11 +1,14 @@
-if vim.g.editorconfig_enable == false or vim.g.editorconfig_enable == 0 then
-  return
-end
-
 local group = vim.api.nvim_create_augroup('editorconfig', {})
 vim.api.nvim_create_autocmd({ 'BufNewFile', 'BufRead', 'BufFilePost' }, {
   group = group,
   callback = function(args)
+    -- Buffer-local enable has higher priority
+    local enable =
+      vim.F.if_nil(vim.b.editorconfig_enable, vim.F.if_nil(vim.g.editorconfig_enable, true))
+    if not enable then
+      return
+    end
+
     require('editorconfig').config(args.buf)
   end,
 })