fix(removeUnknownsAndDefaults): don't strip inherited attrs across ID boundaries - #2241

…ss ID boundaries

Two independent uselessOverrides bugs, both from comparing an attribute
against the parent's full computed style.

1. Inheritance was resolved through the whole ancestor chain, but an
   element with an `id` (or inside `<defs>`/`<symbol>`) may be
   instantiated by `<use>` somewhere else entirely, where the ancestors
   above it do not apply. Stop the walk at that boundary, keeping the
   boundary element itself since it is cloned along with the subtree.

2. The parent's own presentation attributes were all treated as
   inheritable. `presentationNonInheritableGroupAttrs` only covers eight
   of them, so `overflow`, `vector-effect`, `stop-color`, `stop-opacity`,
   `flood-color`, `clip`, `transform-origin` and friends leaked through
   and were dropped from children that legitimately carried them —
   e.g. `overflow` on a nested `<svg>`, which controls its clipping.
   Filter on `inheritableAttrs` instead.

Both views of the cascade are collected in a single ancestor walk.
Each level re-matches the whole stylesheet, so walking twice doubled the
cost of the plugin on deep documents.