Unify with_app_id and with_class methods

Both APIs are used to set application name. This commit unifies the API
between Wayland and X11, so downstream applications can remove platform
specific code when using `WindowBuilderExtUnix`.

Fixes #1739.

src/platform_impl/linux/wayland/window/mod.rs

@@ -159,8 +159,8 @@ impl Window {
         window.set_max_size(max_size);
 
         // Set Wayland specific window attributes.
-        if let Some(app_id) = platform_attributes.app_id {
-            window.set_app_id(app_id);
+        if let Some(name) = platform_attributes.name {
+            window.set_app_id(name.general);
         }
 
         // Set common window attributes.