Apply attributes at every stage

Previously, there was a lot of complicated logic to account for the
fact that certain important attributes might not be added until the end
of the transformation process (via `<书社:apply-attributes>` or
`<书社:apply-attributes-to-root>`). It’s much simpler, conceptually, to
just apply attributes after every transformation phase and not worry
about them besides.

This does mean that if an embed contains an
`<书社:apply-attributes-to-root>` element, it _will_ almost definitely
be applied when·ever that embed is embedded, before the next phase gets
a chance to put a word in edge·wise. Presumably, tho, this is one of
the main utilities of the `<书社:apply-attributes-to-root>` element in
the first place, so maybe that is okay.

This commit introduces a new `书社:finalize` mode for things wot used
to be in the `书社:apply` mode but weren’t actually related to
attribute application.