Converged menu spec (#16517)

* Add new template sections

* Add behaviour sections

* Add comparison

* add samples

* Add behaviour spec

* update behaviour spec

* update spec

* minor fixes

* issues

* fix typos

* add a11y sections

* add links to docsite

* update open/dismiss

* Update specs/Menu.md

Co-authored-by: Juraj Kapsiar <[email protected]>

* add references to wai

* change slot to children

* add right click

* Add basic dom output for comparison

* Add menu divider dom output

* add divider API

* Add expected DOM output

* Add learnings

* add focus specs

* add aria

* add split button proposal

* add missing group

* rework section

* rework split submenu

* add icon examples

* add props

* add secondary label

* convert menu section to group

* update selection sopec

* add a11y warning

* a11y warning

* start prop mapping

* add position alignment hint mapping

* add offset

* add submenu positioning

* add bounds

* Add positioning behaviour

* use menu trigger

* add description for menu triogger

* add migration component variants

Co-authored-by: Juraj Kapsiar <[email protected]>