feat: add sub-menu(s) to CellMenu & ContextMenu plugins

[ghiscoding]

• add sub-menus to all extensions (CellMenu and ContextMenu)
• currently only works by click event on sub-menus, the mouseover will be implemented in a future PR

TODOS

• add full unit test coverage
• add sub-menus to Cell Menu plugin (Example 7)
  • add Cypress E2E tests
• add sub-menus to Context Menu plugin (Example 4)
  • add Cypress E2E tests
• add slick-submenu class when it's a sub-menu
• add sub-menu level number for optional custom styling
  • i.e. Grouping does it in 2 ways: 1-add slick-group-level-2 & 2-add level="2" attribute
• verify that sub-menu(s) is always at an expected position, it seems incorrect for some sub-menus
• add subMenuTitle & subMenuTitleCssClass to optionally add sub-menu title & custom styling
  • must also support translations and add extra subMenuTitleKey and also test with titleKey
• opening a sub-menu then open a sub-menu from another tree doesn't close previous sub-menu that becomes orphan

[codecov]

Codecov Report

Merging #1141 (7586673) into master (1ddee71) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master     #1141    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          245       245            
  Lines        16886     16997   +111     
  Branches      6062      6113    +51     
==========================================
+ Hits         16886     16997   +111     

Files	Coverage Δ
packages/common/src/extensions/extensionUtility.ts	100.00% <100.00%> (ø)
packages/common/src/extensions/menuBaseClass.ts	100.00% <100.00%> (ø)
...ges/common/src/extensions/menuFromCellBaseClass.ts	100.00% <100.00%> (ø)
packages/common/src/extensions/slickCellMenu.ts	100.00% <100.00%> (ø)
packages/common/src/extensions/slickContextMenu.ts	100.00% <100.00%> (ø)
packages/common/src/extensions/slickGridMenu.ts	100.00% <100.00%> (ø)
...ckages/common/src/extensions/slickHeaderButtons.ts	100.00% <100.00%> (ø)
packages/common/src/extensions/slickHeaderMenu.ts	100.00% <100.00%> (ø)