Document the floating ui wrapper

[NullVoxPopuli]

code here:

• https://github.com/universal-ember/ember-primitives/tree/main/ember-primitives/src/floating-ui

example usage:

• https://github.com/universal-ember/ember-primitives/blob/main/ember-primitives/src/components/popover.gts#L216

Note that the Popover component uses this with some nice defaults