content [nfc]: Have resolveUrl return a Uri object, not a String

This pushes the `toString` out to callers, so they can pass the
string form to whatever other code is asking for it.

...Actually, though, in all the cases where that other code has been
asking for the string form, it could easily be changed to accept the
Uri form. So we'll do that, coming up.

Author: chrisbobbe

lib/widgets/content.dart

@@ -224,7 +224,7 @@ class MessageImage extends StatelessWidget {
     return GestureDetector(
       onTap: () {
         Navigator.of(context).push(getLightboxRoute(
-          context: context, message: message, src: resolvedSrc));
+          context: context, message: message, src: resolvedSrc.toString()));
       },
       child: Align(
         alignment: Alignment.centerLeft,
@@ -241,9 +241,9 @@ class MessageImage extends StatelessWidget {
             color: const Color.fromRGBO(0, 0, 0, 0.03),
             child: LightboxHero(
               message: message,
-              src: resolvedSrc,
+              src: resolvedSrc.toString(),
               child: RealmContentNetworkImage(
-                resolvedSrc,
+                resolvedSrc.toString(),
                 filterQuality: FilterQuality.medium))))));
   }
 }
@@ -648,7 +648,7 @@ class MessageImageEmoji extends StatelessWidget {
           // too low.
           top: -1.5,
           child: RealmContentNetworkImage(
-            resolvedSrc,
+            resolvedSrc.toString(),
             filterQuality: FilterQuality.medium,
             width: size,
             height: size,
@@ -823,10 +823,9 @@ class RealmContentNetworkImage extends StatelessWidget {
 /// Resolve `url` to `account`'s realm, if relative
 // This may dissolve when we start passing around URLs as [Uri] objects instead
 // of strings.
-String resolveUrl(String url, Account account) {
+Uri resolveUrl(String url, Account account) {
   final realmUrl = account.realmUrl;
-  final resolved = realmUrl.resolve(url); // TODO handle if fails to parse
-  return resolved.toString();
+  return realmUrl.resolve(url); // TODO handle if fails to parse
 }
 
 InlineSpan _errorUnimplemented(UnimplementedNode node) {

lib/widgets/message_list.dart

@@ -482,7 +482,7 @@ class MessageWithSender extends StatelessWidget {
     final avatar = (avatarUrl == null)
       ? const SizedBox.shrink()
       : RealmContentNetworkImage(
-          avatarUrl,
+          avatarUrl.toString(),
           filterQuality: FilterQuality.medium,
         );