Move from max-width to width for containers, plus a max-width 100%

- Fixes issues between float and flex grid systems where container wouldn't fill the available width in Chrome & FF (but would in Safari)
- Fixes #20681
- Fixes #17621 (basically same issue as above issue)

Author: mdo

scss/mixins/_grid.scss

@@ -17,7 +17,8 @@
 @mixin make-container-max-widths($max-widths: $container-max-widths, $breakpoints: $grid-breakpoints) {
   @each $breakpoint, $container-max-width in $max-widths {
     @include media-breakpoint-up($breakpoint, $breakpoints) {
-      max-width: $container-max-width;
+      width: $container-max-width;
+      max-width: 100%;
     }
   }
 }