[m-rev.] for review: break up inst_util.m and mode_util.m

[Julien Fischer]

On Thu, 16 Dec 2021, Zoltan Somogyi wrote:

>
> 2021-12-15 23:52 GMT+11:00 "Zoltan Somogyi" <zoltan.somogyi at runbox.com>:
>> For review by anyone. There are no changes in code;
>> the only things to be reviewed are the new locations of code,
>> the new comments at the tops of modules, and the new module
>> descriptions in compiler_design.html.
>
> I forgot to mention that there is a ZZZ in the diff, which basically
> raises a fourth issue, which is whether the predicates in inst_util.m
> that operate *only* on types (and *not* on insts) should be moved
> to type_util.m.

Given that type_util is imported by ~100 other modules, not increasing
the size of its interface seems a good reason for leaving the above
predicates where they are.

Julien.