[XCOFF][obj2yaml] Support SymbolAlignmentAndType as 2 separate fields in YAML. (#76828)

XCOFF encodes a symbol type and alignment in a single 8-bit field. It is
easier to read and write YAML files if the fields can be specified
separately. This PR causes obj2yaml to write the fields separately and
allows yaml2obj to read either the single combined field or the separate
fields.