(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/widgets/NewAbstractWidget.ts

@@ -43,7 +43,7 @@ export abstract class NewAbstractWidget extends Disposable {
     )).onWrite((val) => this.field.textColor(val === defaultTextColor ? undefined : val));
     this.fillColor = fromKo(this.field.fillColor);
 
-    this.valueFormatter = fromKo(field.visibleColFormatter);
+    this.valueFormatter = fromKo(field.formatter);
   }
 
   /**