grub: T4548: Fixed configuration files order

To iterate files on ext* file systems GRUB reads their inodes one by one,
ignoring names. This breaks our configuration logic that relies on proper
loading order.

This commit adds a helper sort_inodes() that needs to be used whenever GRUB
configuration files are created. It recreates files, changing their inodes in a
way where inodes order matches alphabetical order.

(cherry picked from commit f74923202311e853b677e52cd83bae2be9605c26)