* Use library for drop modal positioning, fix story

After out-of-tree rendering was implemented for drop-modals, we had
some issues surrounding positioning. By using the `@floating-ui/dom`
library, we can avoid implementing this logic ourselves, and also fix
an overflow scroll bug.

At the same time, this commit fixes the drop-modal story that broke.

Closes https://community.openproject.org/work_packages/46164/activity

* Fix header project select opening direction

After switching to floating-ui/dom, the alignment naming has changed.
This commit fixes the name of the alignment, as well as some eslint errors.

* Fix eslint errors