difference in reuse of lookups for inline liga sub rules

And perhaps for other inline rules as well?

Investigating,

```
python3 -m ttx_diff 'https://github.com/notofonts/lao?ab77daf4d8#sources/NotoSansLao.glyphs'
```

where it looks like we have some overlapping rules that need to be placed in separate lookups, and then when we encounter new non-overlapping rules we are making a different choice about which of the existing lookups to reuse for the new rules.

Contrived example:

```fea
sub a-z B' d' by B_d.one; # create a new liga lookup, 'inline_one'
sub A-Z B' d' by B_d.two; # rule overlaps with above rule; make a new lookup, 'inline_two'
sub one-nine B' x' by B_x; # can reuse either lookup; we choose 'inline_one', fontmake 'inline_two'
```

This should be reasonably easy to fix (*nervous laughter*) and would be preferable to trying to normalize.