Add comments when args span multiple slots

[zbanks]

Follow-up to Simon's suggestion in #198.

For large arguments that span multiple AbiArgSlots, add inline comments indicating their type & offset. This is done using a new CommentExpr wrapper. I also changed the argument names to add the _unk0 if the argument does not fit in one slot, instead of starting with _unk4.

Warn when there are unused subroutine_args for functions with known parameters by including an extra? comment.

Diffs

• The /* extra? */s for create_entity in PM are false positives: the prototype in my context file does not have an ellipsis, unlike the main branch.
• I'm not sure how these arguments should interact with StackInfo.add_known_param(...) -- what type should be used when an argument spans multiple slots? Example: calling right_unk0 a u64 was probably more helpful than calling it a s64, but I don't know how best to generalize this?

[zbanks]

huh, what's up with the missing temp_a1_3 = temp_t7 + 0xFA; in the diff

I screwed up the dependencies function, it's fixed in the next commit.