[query] Refactor vds.sample_qc to use independent aggregators

[chrisvittal]

This will allow expert users to import these functions directly and use them in, for example, grouped aggregators.

from hail.vds.sample_qc import vmt_sample_qc, vmt_sample_qc_variant_annotations

vmt = vds.variant_data
vmt = vmt.annotate_entries(GT=hl.vds.lgt_to_gt(vmt.LGT, vmt.LA))
ac, atype = vmt_sample_qc_variant_annotations(global_gt=vmt.GT, alleles=vmt.alleles)
vmt = vmt.annotate_rows(group=compute_variant_group(vmt), ac=ac, atype=atype)
vmt = vmt.annotate_cols(
    qc=hl.agg.group_by(
        vmt.group,
        vmt_sample_qc(
            global_gt=vmt.GT,
            gq=vmt.GQ,
            ac=vmt.ac,
            atype=vmt.atype,
            dp=vmt.DP
        )
    )
)