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/Token.h

@@ -8,14 +8,10 @@
 
 #include <AK/StringView.h>
 #include <AK/Vector.h>
+#include <LibCMake/Position.h>
 
 namespace CMake {
 
-struct Position {
-    size_t line { 0 };
-    size_t column { 0 };
-};
-
 struct VariableReference {
     StringView value;
     Position start;