fix: use shared modal manager to sync container state

[kyletsang]

Fixes #5905

This fix uses a shared ModalManager between Offcanvas and Modal in order to sync the container state in the scenario where you can trigger the closing/opening of both Offcanvas and Modal at the same time. In the case where the Offcanvas has the scroll prop set to true, we use a local ModalManager because the shared one handles overflow styles. I think this should be ok since we don't need to modify the container styles when scroll is true.

This also fixes some differences in behavior compared to upstream bootstrap where enforce focus should not be enabled when scroll is enabled for Offcanvas. The user should be able to select text, or focus outside. In addition, clicking outside Offcanvas should not close the Offcanvas when backdrop is false: https://getbootstrap.com/docs/5.0/components/offcanvas/#backdrop