Summary:
- When importing into a Ref column, use lookupOne() formula for correct previews.
- When selecting columns to import into a Ref column, now a Numeric column like
'Order' will produce two options: "Order" and "Order (as row ID)".
- Fixes exports to correct the formatting of visible columns. This addresses multiple bugs:
1. Formatting wasn't used, e.g. a Ref showing a custom-formatted date was still presented as YYYY-MM-DD in CSVs.
2. Ref showing a Numeric column was formatted as if a row ID (e.g. `Table1[1.5]`), which is very wrong.
- If importing into a table that doesn't have a primary view, don't switch page after import.
Refactorings:
- Generalize GenImporterView to be usable in more cases; removed near-duplicated logic from node side
- Some other refactoring in importing code.
- Fix field/column option selection in ValueParser
- Add NUM() helper to turn integer-valued floats into ints, useful for "as row ID" lookups.
Test Plan: Added test cases for imports into reference columns, updated Exports test fixtures.
Reviewers: georgegevoian
Reviewed By: georgegevoian
Differential Revision: https://phab.getgrist.com/D3875
