(core) Context menu for cards.

Summary:
User was not able to delete cards. This patch introduces a context menu for cards, analogous to the one available for rows on a GridView.

Changes:
- Row numbers on a GridView have the same icon as on columns to make context menu more discoverable.
- Context menu for rows and columns, when activated, didn't switch section in rare conditions (i.e. when the section had 2 or more columns selected, one of which had the same rowId as a column in the section that the user switched from).
- Card list layout and a single card layout has the same context menu as in a GridView, available by pressing the context menu button.

Test Plan: Browser tests

Reviewers: dsagal, paulfitz

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2870

app/client/ui/RowContextMenu.ts

@@ -0,0 +1,38 @@
+import { allCommands } from 'app/client/components/commands';
+import { menuDivider, menuItemCmd } from 'app/client/ui2018/menus';
+import { dom } from 'grainjs';
+
+interface IRowContextMenu {
+  disableInsert: boolean;
+  disableDelete: boolean;
+  isViewSorted: boolean;
+}
+
+export function RowContextMenu({ disableInsert, disableDelete, isViewSorted }: IRowContextMenu) {
+  const result: Element[] = [];
+  if (isViewSorted) {
+    // When the view is sorted, any newly added records get shifts instantly at the top or
+    // bottom. It could be very confusing for users who might expect the record to stay above or
+    // below the active row. Thus in this case we show a single `insert row` command.
+    result.push(
+      menuItemCmd(allCommands.insertRecordAfter, 'Insert row',
+        dom.cls('disabled', disableInsert)),
+    );
+  } else {
+    result.push(
+      menuItemCmd(allCommands.insertRecordBefore, 'Insert row above',
+        dom.cls('disabled', disableInsert)),
+      menuItemCmd(allCommands.insertRecordAfter, 'Insert row below',
+        dom.cls('disabled', disableInsert)),
+    );
+  }
+  result.push(
+    menuDivider(),
+    menuItemCmd(allCommands.deleteRecords, 'Delete',
+      dom.cls('disabled', disableDelete)),
+  );
+  result.push(
+    menuDivider(),
+    menuItemCmd(allCommands.copyLink, 'Copy anchor link'));
+  return result;
+}