A metadata builder that cannot register new field names, and merely returns the field id
associated with a known field name. This is useful for variant unshredding operations, where the
metadata column is fixed and – per variant shredding spec – already contains all field names
from the typed_value column. It is also useful when projecting a subset of fields from a variant
object value, since the bytes can be copied across directly without re-encoding their field ids.
A trait for building variant metadata dictionaries, to be used in conjunction with a
ValueBuilder. The trait provides methods for managing field names and their IDs, as well as
rolling back a failed builder operation that might have created new field ids.