add matrix: URI deeplinking

Fixes #148

Needs cross-platform testing, currently only tested on Android.

lib/helpers/extensions/open_link_info.dart

@@ -0,0 +1,49 @@
+import "package:material_ui/material_ui.dart";
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:nexus/controllers/event.dart";
+import "package:nexus/controllers/room_summary.dart";
+import "package:nexus/helpers/extensions/focus_room.dart";
+import "package:nexus/helpers/extensions/get_link_info.dart";
+import "package:nexus/helpers/extensions/show_adaptive_sheet.dart";
+import "package:nexus/helpers/extensions/show_user_popover.dart";
+import "package:nexus/models/room_summary.dart";
+import "package:nexus/widgets/room_summary_sheet.dart";
+
+extension OpenLinkInfo on WidgetRef {
+  Future<void> openLinkInfo(
+    BuildContext context,
+    LinkInfo linkInfo, {
+    String? roomId,
+  }) async {
+    final identifier = linkInfo.identifier;
+    if (identifier.startsWith("@")) {
+      context.showUserPopover(identifier, roomId: roomId);
+      return;
+    }
+
+    final request = RoomSummaryController.provider(
+      .new(roomIdOrAlias: identifier, via: linkInfo.via),
+    );
+    final summary = await read(request.future)
+        .onError((_, _) => RoomSummary(roomId: identifier));
+
+    final eventRowId = linkInfo.eventId == null
+        ? null
+        : await read(
+            EventController.provider(
+              .new(roomId: summary.roomId, eventId: linkInfo.eventId!),
+            ).selectAsync((data) => data?.rowId),
+          ).onError((_, _) => null);
+
+    if (await focusRoom(summary.roomId, eventRowId) || !context.mounted) return;
+
+    await context.showAdaptiveSheet(
+      (context) => Consumer(
+        builder: (context, ref, _) => RoomSummarySheet(
+          ref.watch(request).whenOrNull(data: (data) => data) ?? summary,
+          via: linkInfo.via,
+        ),
+      ),
+    );
+  }
+}