get_default_style did an exact-name map lookup, so subtypes like
IfcWallStandardCase or IfcSlabStandardCase never inherited the default
material of their parent type, falling through to the generic grey
DefaultMaterial instead. This was reported in 2018 (#473) and the fix
direction (walk up the supertype chain once the schema runtime made
supertypes available) was agreed there, but never implemented.
On an exact-match miss the lookup now walks decl->supertype() until a
mapped ancestor is found, caching the result under the leaf name for
O(1) subsequent lookups. The product's user-facing type string is
deliberately untouched; only the style lookup gained inheritance.
Applies equally to the built-in defaults and --default-material-file.
This change was written with AI assistance.
Petru Conduraru