* create responsive containers

provide more flexibility and allow the user to determine when containers switch from fluid to fixed width.

* fix the base container code

this commit fixes the non-media portion of the generated CSS. I learned about the `@extends` directive and was able to put it to good use.

I create a new temporary map that contains all the main `$container-max-widths` and join it to our 2 special cases of 'xs' and 'fluid'.  Then we loop through that and, with the appropriate infixes, extend our placeholder

* formatting for style

forgot to run my tests before the last push, i think these are better.

* finish incomplete comment

* fix the responsive containers

using the `@extend` directive I was able to clean up this code

* fix responsive containers in the navbar

mostly we just look through all of our breakpoints so we can include all of the responsive container classes in the tweaks we have to do for the navbar (redec...

* Use escape-svg() function

* Update theming.md

This is a link.

Fixes #26563, closes #26576, closes #29021.

Fixes IE.

Also use `viewBox` instead of `viewbox`.

Held babel back due to issues with `objectSpread`.