Browser: Store default config values in a single place

Note that this fixes contradictory default values for group
"Preferences", key "Home". This is exactly the kind of errors I want to
prevent with this new style.

The hope is that this can later be used to:
- verify that all accesses to the same key use the same default value,
- and extract the default values more easily.

Userland/Applications/BrowserSettings/Defaults.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2023, Ben Wiederhake <BenWiederhake.GitHub@gmx.de>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/StringView.h>
+
+namespace Browser {
+
+static constexpr StringView default_homepage_url = "file:///res/html/misc/welcome.html"sv;
+static constexpr StringView default_new_tab_url = "file:///res/html/misc/new-tab.html"sv;
+static constexpr StringView default_search_engine = ""sv;
+static constexpr StringView default_color_scheme = "auto"sv;
+static constexpr bool default_enable_content_filters = true;
+static constexpr bool default_show_bookmarks_bar = true;
+static constexpr bool default_close_download_widget_on_finish = false;
+static constexpr bool default_allow_autoplay_on_all_websites = false;
+
+}