(core) Adding new command Duplicate rows

Summary:
New command "Duplicate rows" is available in the Row/Card Context Menu and as a keyboard shortcut Ctrl+Alt+C.
- All selected rows are duplicated (even if only a single column is selected)
- Rows are inserted immediately after the last selected row (using manualSort value).
- Formulas and CENSORED fields are not copied.
Implemented on the UI level (no new action).

Test Plan: new test

Reviewers: cyprien

Reviewed By: cyprien

Differential Revision: https://phab.getgrist.com/D3371

app/client/components/DetailView.js

@@ -216,6 +216,7 @@ DetailView.prototype.buildContextMenu = function(row, options) {
     disableInsert: Boolean(this.gristDoc.isReadonly.get() || this.viewSection.disableAddRemoveRows() || this.tableModel.tableMetaRow.onDemand()),
     disableDelete: Boolean(this.gristDoc.isReadonly.get() || this.viewSection.disableAddRemoveRows() || row._isAddRow()),
     isViewSorted: this.viewSection.activeSortSpec.peek().length > 0,
+    numRows: this.getSelection().rowIds.length,
   };
   return RowContextMenu(options ? Object.assign(defaults, options) : defaults);
 }
@@ -422,4 +423,9 @@ DetailView.prototype.scrollToCursor = function(sync = true) {
   return kd.doScrollChildIntoView(this.scrollPane, this.cursor.rowIndex(), sync);
 }
 
+DetailView.prototype._duplicateRows = async function() {
+  const addRowIds = await BaseView.prototype._duplicateRows.call(this);
+  this.setCursorPos({rowId: addRowIds[0]})
+}
+
 module.exports = DetailView;