Dropdown: support dynamic popper on navbar

[GeoSot]

Support popper configurations on navbar dynamically.

Changes:

• we do not search for navbar parents
• popper can handle the element style, during resizing
• we gain :
  • popper offsetconfiguration, while we have dynamic positioned dropdown
  • popper preventOverflow functionality on navbar dropdowns

~~Preview:~~ ~~https://deploy-preview-35901--twbs-bootstrap.netlify.app/docs/5.1/examples/headers/~~ ~~(I have added the previously not working example on preview, adding offset)~~

@mdo & @twbs/css-review I will need your help on this, in case I am missing something

Todo:

• [x] fix/add tests
• [x] revert headers example

Closes #35397 Closes #34471 and Closes #33957 closes #36897 closes #36789

[mrleblanc101]

What prevents this from being merged ?