(core) Reference and ReferenceList formatters

Summary:
Previously, ref/reflist columns were formatted entirely based on their visible column, since they received values from the visible or display columns rather than the actual row IDs. This creates `ReferenceFormatter` and `ReferenceListFormatter` which still delegate most of the formatting work to a visible column formatter but fix a few issues:

- ReferenceList columns now actually use the options (e.g. date format) of the visible column to format their elements. Previously they were formatted generically because the visible column formatter wasn't expecting a list.
- Invalid references aren't formatted with an `#Invalid Ref` prefix.
- When the ref column displays the Row ID, it doesn't have a visible or display column. Previously this led to the references being formatted as just numbers in most cases, with special code in the widget to display them like `Table1[2]`. Now they are consistently formatted in that style throughout.

Test Plan: Updated existing tests.

Reviewers: jarek

Reviewed By: jarek

Subscribers: dsagal

Differential Revision: https://phab.getgrist.com/D3212

app/client/models/SearchModel.ts

@@ -218,7 +218,7 @@ class FinderImpl implements IFinder {
     this._sectionTableData = tableModel.tableData;
 
     this._fieldStepper.array = section.viewFields().peek();
-    this._fieldFormatters = this._fieldStepper.array.map(f => f.visibleColFormatter.peek());
+    this._fieldFormatters = this._fieldStepper.array.map(f => f.formatter.peek());
     return tableModel;
   }