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/Position.h

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2023, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+
+namespace CMake {
+
+struct Position {
+    size_t line { 0 };
+    size_t column { 0 };
+};
+
+}