LibCMake: Add a lexer for CMakeCache.txt

This is a totally different syntax than for regular CMake files, and
also is undocumented and subject to change, but it's also nice and
simple. :^)

Userland/Libraries/LibCMake/CMakeCache/Token.h

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2023, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibCMake/Position.h>
+
+namespace CMake::Cache {
+
+struct Token {
+    enum class Type {
+        Comment,
+        HelpText,
+        Key,
+        Colon,
+        Type,
+        Equals,
+        Value,
+        Garbage,
+    };
+    Type type;
+    StringView value;
+
+    Position start;
+    Position end;
+};
+
+static constexpr StringView to_string(Token::Type type)
+{
+    switch (type) {
+    case Token::Type::Comment:
+        return "Comment"sv;
+    case Token::Type::HelpText:
+        return "HelpText"sv;
+    case Token::Type::Key:
+        return "Key"sv;
+    case Token::Type::Colon:
+        return "Colon"sv;
+    case Token::Type::Type:
+        return "Type"sv;
+    case Token::Type::Equals:
+        return "Equals"sv;
+    case Token::Type::Value:
+        return "Value"sv;
+    case Token::Type::Garbage:
+        return "Garbage"sv;
+    }
+
+    VERIFY_NOT_REACHED();
+}
+
+}