Add auto-positioning for our toast component

Created by: Johann-S

Changes:

• added auto positioning for our toast component (top-center, top-left, top-right, bottom-center, bottom-left, bottom-right).
• Removed the use of .hide because I cannot get elements widths

TODO:

• Top middle
• Bottom middle
• Docs
• Unit tests
• Fix docs example situation while a toast is still showing
• Revisit the apply styles at once approach
• Add migration notes

You can test it here:

• https://deploy-preview-28783--twbs-bootstrap.netlify.app/docs/5.0/components/toasts/#placement
• https://codepen.io/Johann-S/pen/BedGrO