Migrate from Popper to Floating UI

[mdo]

WIP, need to edit description more for changes.

All components

• Drops Popper for Floating UI across dropdowns, popovers, and tooltips
• Replaces all references to Popper with Floating UI
• Removes static positioning on dropdowns in navbars
• Updates page filenames to be singular for components (more to do for consistency later)
• New way to responsively set alignment, using prefix breakpoints in the placement data attribute (e.g., data-bs-placement="bottom-start md:bottom-end")

Dropdowns

• New styles for dropdown items, headings, and dividers
• Menus now use flexbox (column) with a gap between items
• No more dropup, dropend, dropstart, etc—just .dropdown.
• No more carets by default on .dropdown-toggle.

Popovers & Tooltips

• data-popper-placement is now data-bs-placement
• Refined font, padding, and other styles for both components

[Remzi1993]

@mdo I understand this is an old merge request, but I would like to highlight that it would have been better if developers who use Bootstrap (like me) could independently update Floating UI, otherwise we're all depended on Bootstrap to keep up to date with Floating UI, while if it was shipped as an optional add on you need to install yourself then it would be much easier for us to keep it up to date. It would also lessen the burden on the Bootstrap team.