Revert "Revert "[fuchsia] Add diagnostics directory to the set of remote dirs (#14470)" (#14566)"

This reverts commit 4312d37.

Once https://fuchsia-review.googlesource.com/c/topaz/+/351729 lands, the
diagnostics directory will be present, this would be safe to do and the
roller won't be blocked again.

Author: miguelfrde

shell/platform/fuchsia/flutter/component.cc

@@ -233,7 +233,7 @@ Application::Application(
                          << "): " << zx_status_get_string(status);
           return;
         }
-        const char* other_dirs[] = {"debug", "ctrl"};
+        const char* other_dirs[] = {"debug", "ctrl", "diagnostics"};
         // add other directories as RemoteDirs.
         for (auto& dir_str : other_dirs) {
           fidl::InterfaceHandle<fuchsia::io::Directory> dir;