bug#66702: Add easy customization for .dir-locals.el files

[Juri Linkov]

>> I tried it out on emacs/.dir-locals.el, and one thing that I noticed is that
>> it changes the order of modes by sorting them alphabetically.  I'm sure
>> people won't like if their files will get so much changes especially
>> when they intend to commit a change in a single value.
>
> That's modify-dir-local-variable doing the sorting.
>
> You get the same results by doing:
> emacs -Q
> M-x add-dir-local-variable RET nil RET foo RET t
> M-x diff-buffer-with-file RET RET
>
> Should we add a nosort option somewhere?

The assumption was that .dir-locals.el will always be modified
by these commands.  But since it's often modified manually
with an arbitrary order, this means that the sorting order
is not important.  So we could simply remove the sorting code.

PS: This is not directly related to your current patch that I believe
is ready to be installed if no one will have more comments.