Currently we configure per-field postings formats by asking the MapperService
for the MappedFieldType of the field in question, and then checking to see if it
is a completion field. If no MappedFieldType is available, we emit a warning.
However, MappedFieldTypes are for search fields only, and so we end up emitting
warnings for hidden sub-fields that have no corresponding field type, such as
prefix or phrase accelerator fields on text mappers.
This commit reworks things so that the MappingLookup is responsible for defining
per-field postings formats, and will detect CompletionFieldMappers at build time.
All fields that are not mapped to a completion field will just get the default postings
format. This also means that we no longer need a logger instance on CodecService.
Fixes#77183
385b97f92b