Provides compatibility loading older files outside the context of
a library.
Older material files were loaded by specifying a path. The new
material system used the path to associated the material with a
library, which may not be appropriate for legacy files. This change
allows the use of materials outside of a library.
Additionally, legacy files often have name/value pairs not part of the
standard list of properties. Since these were unable to be mapped to
a model property they were ignored. Materials now maintain a legacy
map to hold properties not associated with a property model. These
properties are considered transient and will not be saved. It is not
intended for this feature to be used as a generic container for
properties not mapped to an appropriate model.
Fixes#13302
f950a0c086