In the import modal `Specify Fields and Types` table, add a skeleton loading status while we analyze the CSV fields and types. Let's reuse the skeleton we show for the collections tree.
In this work we start running `analyzeCSVFields`. Add a `mixed` data type field. This is also re-run when the delimiter is re-selected. We'll already have the first few csv fields, however we can't pre-select the types until we've analyzed the csv fields.