Summary:
- Brings in a new utility `contextMenu` to open context menu next to the mouse position
- Use this utility to show a CellContextMenu, that sort of merge cell context menu and column context menu together.
- Show cell context menu on context click on any grid's cell.
- Also takes care of showing the row context menu for detail view on a context click that occurs on cells and not only on the row num header as it was the case prior to this diff.
- task: https://gristlabs.getgrist.com/doc/check-ins/p/5#a1.s9.r1529.c31
- discussion: https://grist.quip.com/ETGkAroLnc0Y/Cell-Context-Menu
{F40092}
Test Plan: - Adds project test and nbrowser for cell context menu and new cases for the detail row context menu.
Reviewers: jarek
Reviewed By: jarek
Differential Revision: https://phab.getgrist.com/D3237
