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

[Zoltan Somogyi]

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.

Zoltan.