recent dms [nfc]: Handle bottom insets explicitly in recent DMs page

This reverts part of 742320c for RecentDmConversationsPageBody,
and also handles bottom insets for the list view and the new DMs
button.

As this widget is planned to be used outside the context of home
page, specifically for the upcoming share page.

Author: rajveermalviya

lib/widgets/recent_dm_conversations.dart

@@ -73,9 +73,20 @@ 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.
+            //
+            // When this page is used in the context of the home page, this
+            // param and the below use of `MediaQuery.paddingOf(context).bottom`
+            // would be noop, because `Scaffold.bottomNavigationBar` in the
+            // home page handles that for us. But this page is planned to be
+            // used for share-to-zulip page, so we need this to be handled here.
+            //
+            // Other *PageBody widgets don't handle this because they aren't
+            // planned to be (re-)used outside the context of the home page.
+            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 +115,7 @@ class _RecentDmConversationsPageBodyState extends State<RecentDmConversationsPag
                     });
               })),
         Positioned(
-          bottom: 21,
+          bottom: MediaQuery.paddingOf(context).bottom + 21,
           child: _NewDmButton(onDmSelect: widget.onDmSelect)),
       ]);
   }