content: Use directional layout for block quotations

Previously, the `Quotation` widget hardcoded the border and padding
to the left side. This resulted in an incorrect layout in RTL
locales, where the quote bar remained on the left while the text
aligned to the right.

We now use `EdgeInsetsDirectional` and `BorderDirectional` so that
the layout flips correctly based on the text direction.

Suggested by @gnprice.

Author: yash-agarwa-l

lib/widgets/content.dart

@@ -468,12 +468,12 @@ class Quotation extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Padding(
-      padding: const EdgeInsets.only(left: 10),
+      padding: const EdgeInsetsDirectional.only(start: 10),
       child: Container(
-        padding: const EdgeInsets.only(left: 5),
+        padding: const EdgeInsetsDirectional.only(start: 5),
         decoration: BoxDecoration(
-          border: Border(
-            left: BorderSide(
+          border: BorderDirectional(
+            start: BorderSide(
               width: 5,
               // Web has the same color in light and dark mode.
               color: const HSLColor.fromAHSL(1, 0, 0, 0.87).toColor()))),