(core) Initial data tables page

Summary:
- Added a new special page for viewing raw data widgets:
  - Implemented in DataTables.ts
  - Accessible only via the special URL path `/p/data`
  - Future diffs should make this page prettier and easily accessible
  - Shows a list of user tables
  - Clicking on a table name shows its `rawViewSection` by setting `GristDoc.viewModel.activeSectionId`. Note that in this case `GristDoc.viewModel` is an empty record, so this is a bit of a hack, but it works well and causes no known issues.
- Added `ViewSectionRec.isRaw` to know if the record represents a raw data widget.
- Added various restrictions in the UI for raw data widgets:
  - 'Delete widget' is disabled in the 3-dot widget menu.
  - Prevent hiding columns:
    - "Hide column" in the column context menu is disabled
    - The "VISIBLE/HIDDEN COLUMNS" section of the right panel > Table > Widget is hidden
  - The toggle bar isn't configurable to ensure that users know when raw data is filtered:
    - The filter bar always shows if and only if some filters are present
    - "Toggle Filter Bar" is hidden in:
      - Right panel > Table > Sort & Filter
      - The sort/filter menu next to the three-dot menu for widgets.
  - Other restrictions in the right panel:
    - In the Column tab:
      - 'Use separate settings' is disabled
    - In the Table tab:
      - In the Widget subtab:
        - 'Change Widget' is hidden
      - In the Data subtab:
        - 'Edit Data Selection' is hidden
        - 'SELECT BY' is hidden

Test Plan: Tested manually. The behaviour of raw data widgets may still change and they aren't easily visible to users yet.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3248

app/client/components/DataTables.ts

@@ -0,0 +1,32 @@
+import {GristDoc} from 'app/client/components/GristDoc';
+import {buildViewSectionDom, ViewSectionHelper} from 'app/client/components/ViewLayout';
+import {ViewSectionRec} from 'app/client/models/DocModel';
+import {Disposable, dom, domComputed} from 'grainjs';
+
+export class DataTables extends Disposable {
+  constructor(private _gristDoc: GristDoc) {
+    super();
+  }
+
+  public buildDom() {
+    return [
+      dom(
+        'ul',
+        this._gristDoc.docModel.allTables.all().map(t => dom(
+          'li', t.rawViewSection().title() || t.tableId(),
+          dom.on('click', () => this._gristDoc.viewModel.activeSectionId(t.rawViewSection.peek().getRowId())),
+        ))
+      ),
+      domComputed<ViewSectionRec>(
+        this._gristDoc.viewModel.activeSection,
+        (viewSection) => {
+          if (!viewSection.getRowId()) {
+            return;
+          }
+          ViewSectionHelper.create(this, this._gristDoc, viewSection);
+          return buildViewSectionDom(this._gristDoc, viewSection.getRowId());
+        }
+      )
+    ];
+  }
+}