Working similarly to addExons, this function
can be used to add information about CDS (coding sequence)
to the SummarizedExperiment object. As not all transcripts
are coding, we have CDS information for only a subset of the
rows of the object. For this reason, a logical indicator for
whether the transcript is coding, mcols(se)$coding,
is added as a column to the metadata columns of the rowRanges
of the object. An additional column, mcols(se)$cds,
is added to the metadata columns, which is a GRangesList
with either the CDS regions (if the transcript is coding),
or the original transcript/exon ranges (if the transcript is non-coding).
This is necessary, as GRangesList cannot have NA elements.
As with addExons, this function is designed only
for transcript-level objects.
addCDS(se)a SummarizedExperiment