Add vim.cmd as an alias for nvim_command (#11446)

src/nvim/lua/vim.lua

@@ -277,6 +277,10 @@ setmetatable(vim, {
   __index = __index
 })
 
+-- An easier alias for commands.
+vim.cmd = vim.api.nvim_command
+
+-- These are the vim.env/v/g/o/bo/wo variable magic accessors.
 do
   local a = vim.api
   local validate = vim.validate