LibGUI: Add IncrementalSearchBanner

Compared to traditional modal search, incremental search begins
matching as soon as the user starts typing, highlighting results
immediately. This refactors Itamar's work for HackStudio into a
common LibGUI widget to be used in all multi-line TextEditors.

Userland/Libraries/LibGUI/IncrementalSearchBanner.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2022, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGUI/TextEditor.h>
+#include <LibGUI/Widget.h>
+
+namespace GUI {
+
+class IncrementalSearchBanner final : public Widget {
+    C_OBJECT(IncrementalSearchBanner);
+
+public:
+    virtual ~IncrementalSearchBanner() override = default;
+
+    void show();
+    void hide();
+
+protected:
+    explicit IncrementalSearchBanner(TextEditor&);
+
+    virtual void paint_event(PaintEvent&) override;
+    virtual Optional<UISize> calculated_min_size() const override;
+
+private:
+    void search(TextEditor::SearchDirection);
+
+    NonnullRefPtr<TextEditor> m_editor;
+    RefPtr<Button> m_close_button;
+    RefPtr<Button> m_next_button;
+    RefPtr<Button> m_previous_button;
+    RefPtr<Button> m_wrap_search_button;
+    RefPtr<Button> m_match_case_button;
+    RefPtr<Label> m_index_label;
+    RefPtr<TextBox> m_search_textbox;
+
+    TextDocument::SearchShouldWrap m_wrap_search { true };
+    bool m_match_case { false };
+};
+
+}