CharacterMap: Add a find-by-name window

This works the same way as the command-line usage, searching against the
display name as provided by LibUnicode.

I've modified the search loop to cover every possible unicode
code-point, since my previous logic was flawed. Code-points are not
dense, there are gaps, so simply iterating up to the count of them will
skip ones with higher values. Surprisingly, iterating all 1,114,112 of
them still runs in a third of a second. Computers are fast!

Userland/Applications/CharacterMap/CharacterSearchWidget.h

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include "CharacterMapWidget.h"
+#include <LibGUI/Button.h>
+#include <LibGUI/ListView.h>
+#include <LibGUI/TextBox.h>
+
+class CharacterSearchWidget final : public GUI::Widget {
+    C_OBJECT(CharacterSearchWidget);
+
+public:
+    virtual ~CharacterSearchWidget() override;
+
+    Function<void(u32)> on_character_selected;
+
+private:
+    CharacterSearchWidget();
+
+    void search();
+
+    RefPtr<GUI::TextBox> m_search_input;
+    RefPtr<GUI::Button> m_search_button;
+    RefPtr<GUI::ListView> m_results_list;
+};