8248/fix toc layout (#8338)

This PR adjusts the page padding site wide to ensure that the minimum
breakpoint at which the TOC appears allows embedded examples to show the
default desktop breakpoint. Previously this would show a tablet
breakpoint instead.
* Updated Page styles to reduce gap from `5rem` to `2.5rem` 
* Update Container styles to reduce horizontal padding from `4rem` to
`1.5rem`

Author: gwyneplaine

polaris.shopify.com/src/components/Container/Container.module.scss

@@ -5,7 +5,7 @@
   margin-left: auto;
   margin-right: auto;
   max-width: $pageMaxWidth;
-  padding: 0 4rem;
+  padding: 0 1.5rem;
 
   @media screen and (max-width: $breakpointTablet) {
     padding: 0 1.25rem;

polaris.shopify.com/src/components/Page/Page.module.scss

@@ -23,7 +23,7 @@
 .Page {
   --toc-width: 16rem;
   display: flex;
-  gap: 5rem;
+  gap: 2.5rem;
 }
 
 .Post {