Function idea: Convert CELLxGENE AnnData to SCE

We have encountered a few times where we've had to convert from AnnData -> SCE, in particular when using AnnData files from CELLxGENE. One not immediately intuitive aspect of this is, after initial conversion with zellkonverter, the raw counts are stored in an altExp called `raw` as an assay named `X`, rather than as a `counts` assay in the main SCE experiment. Similarly although more intuitively, logcounts are stored in the `X` assay of the main experiment. There are also `X_` prefixes in the reduced dimensions.

We might consider writing a wrapper function to assist in performing this specific CELLxGENE AnnData -> SCE conversion that takes its particular data structure into consideration and returns an SCE object with slots labeled analogously to ScPCA data.

No file or test is named. Start by reviewing zellkonverter's AnnData-to-SCE result and the ScPCA data structure described in the issue; done means a wrapper returns an SCE with raw counts, logcounts, and reduced dimensions labeled analogously to ScPCA data.

Written by the indexing model from the issue text.