LibSyntax+Userland: Make LibSyntax not depend on LibGUI

This moves some stuff around to make LibGUI depend on LibSyntax instead
of the other way around, as not every application that wishes to do
syntax highlighting is necessarily a LibGUI (or even a GUI) application.

Userland/Libraries/LibSyntax/TextRange.h

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022-2023, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibSyntax/TextPosition.h>
+
+namespace Syntax {
+
+class TextRange {
+public:
+    TextRange() = default;
+    TextRange(TextPosition const& start, TextPosition const& end)
+        : m_start(start)
+        , m_end(end)
+    {
+    }
+
+    bool is_valid() const { return m_start.is_valid() && m_end.is_valid() && m_start != m_end; }
+    void clear()
+    {
+        m_start = {};
+        m_end = {};
+    }
+
+    TextPosition& start() { return m_start; }
+    TextPosition& end() { return m_end; }
+    TextPosition const& start() const { return m_start; }
+    TextPosition const& end() const { return m_end; }
+
+    size_t line_count() const { return normalized_end().line() - normalized_start().line() + 1; }
+
+    TextRange normalized() const { return TextRange(normalized_start(), normalized_end()); }
+
+    void set_start(TextPosition const& position) { m_start = position; }
+    void set_end(TextPosition const& position) { m_end = position; }
+
+    void set(TextPosition const& start, TextPosition const& end)
+    {
+        m_start = start;
+        m_end = end;
+    }
+
+    bool operator==(TextRange const& other) const
+    {
+        return m_start == other.m_start && m_end == other.m_end;
+    }
+
+    bool contains(TextPosition const& position) const
+    {
+        if (position.line() <= m_start.line() && (position.line() != m_start.line() || position.column() < m_start.column()))
+            return false;
+        if (position.line() >= m_end.line() && (position.line() != m_end.line() || position.column() > m_end.column()))
+            return false;
+        return true;
+    }
+
+private:
+    TextPosition normalized_start() const { return m_start < m_end ? m_start : m_end; }
+    TextPosition normalized_end() const { return m_start < m_end ? m_end : m_start; }
+
+    TextPosition m_start {};
+    TextPosition m_end {};
+};
+
+}
+
+template<>
+struct AK::Formatter<Syntax::TextRange> : AK::Formatter<FormatString> {
+    ErrorOr<void> format(FormatBuilder& builder, Syntax::TextRange const& value)
+    {
+        if (value.is_valid())
+            return Formatter<FormatString>::format(builder, "{}-{}"sv, value.start(), value.end());
+        return builder.put_string("TextRange(Invalid)"sv);
+    }
+};