(core) New chart view axis conf with picker for each of X,Y and group by

Summary:
Chart view used to rely on the same view field configuration as used in any other widget.

This diff allows to explicitely select X-AXIS, Y-AXIS and group by column with column picker.

As charts supports several y-axis, we still use a draggable list to arrange them.

Diff also fix doc to the `insertPositions` function.

Test Plan: Updated the relevant test.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3021

app/client/ui/RightPanel.ts

@@ -334,8 +334,10 @@ export class RightPanel extends Disposable {
         }
       ]),
 
-      cssSeparator(),
-      dom.create(VisibleFieldsConfig, this._gristDoc, activeSection, true)
+      dom.maybe((use) => use(this._pageWidgetType) !== 'chart', () => [
+        cssSeparator(),
+        dom.create(VisibleFieldsConfig, this._gristDoc, activeSection, true),
+      ]),
     ]);
   }
 
@@ -650,7 +652,7 @@ const cssTabContents = styled('div', `
   overflow: auto;
 `);
 
-const cssSeparator = styled('div', `
+export const cssSeparator = styled('div', `
   border-bottom: 1px solid ${colors.mediumGrey};
   margin-top: 16px;
 `);