home [nfc]: Handle safe-area in recent DMs and subscription list page

This reverts part of 742320c for RecentDmConversationsPageBody
and SubscriptionListPageBody, as these widgets will soon be used
outside the context of home page, specifically for the upcoming
share page.

The other *PageBody widgets, currently only InboxPageBody, don't
need these as they aren't used outside the context of the home
page.

Author: rajveermalviya

lib/widgets/recent_dm_conversations.dart

@@ -73,9 +73,11 @@ class _RecentDmConversationsPageBodyState extends State<RecentDmConversationsPag
           PageBodyEmptyContentPlaceholder(
             message: zulipLocalizations.recentDmConversationsEmptyPlaceholder)
         else
-          SafeArea( // horizontal insets
+          SafeArea(
+            // Don't pad the bottom here; we want the list content to do that.
+            bottom: false,
             child: ListView.builder(
-              padding: EdgeInsets.only(bottom: 90),
+              padding: EdgeInsets.only(bottom: MediaQuery.paddingOf(context).bottom + 90),
               itemCount: sorted.length,
               itemBuilder: (context, index) {
                 final narrow = sorted[index];
@@ -104,7 +106,7 @@ class _RecentDmConversationsPageBodyState extends State<RecentDmConversationsPag
                     });
               })),
         Positioned(
-          bottom: 21,
+          bottom: MediaQuery.paddingOf(context).bottom + 21,
           child: _NewDmButton(onDmSelect: widget.onDmSelect)),
       ]);
   }

lib/widgets/subscription_list.dart

@@ -119,7 +119,9 @@ class _SubscriptionListPageBodyState extends State<SubscriptionListPageBody> wit
         message: zulipLocalizations.channelsEmptyPlaceholder);
     }
 
-    return SafeArea( // horizontal insets
+    return SafeArea(
+      // Don't pad the bottom here; we want the list content to do that.
+      bottom: false,
       child: CustomScrollView(
         slivers: [
           if (pinned.isNotEmpty) ...[
@@ -140,6 +142,9 @@ class _SubscriptionListPageBodyState extends State<SubscriptionListPageBody> wit
           ],
 
           // TODO(#188): add button leading to "All Streams" page with ability to subscribe
+
+          // This ensures last item in scrollable can settle in an unobstructed area.
+          const SliverSafeArea(sliver: SliverToBoxAdapter(child: SizedBox.shrink())),
         ]));
   }
 }