This works per-syllable as per the spec, but we think it should be per
spacing/base/??? glyph instead.

Use it in USE.

Same logic as in Indic shaper.

Same logic as Indic and SEA.

These were never tested with Indic shaper, and indeed wouldn't work there
because they didn't have their viramas and other config defined.  They are
all also supported by MS through USE, so route them there.

This makes USE feature-complete as far as the Indic-like features
are concerned.

Unused right now.

And add check to FLAG()

Still no reordering.

Don't reroute scripts that we were routing to other shapers
before (just yet).

Even compiles.

Positional sub-categories not applied yet.

The spec wrongly has "H" where "HN" is meant.

Grammar from the spec!