Make the C++ Value API a little less error prone

Yesterday I ended up accidentally constructing a Value with a string literal
and that turned into a boolean value, resulting in run-time panic.
A deleted `const void *` constructor prevents this by producing a compile error instead of
picking the boolean constructor.

api/sixtyfps-cpp/include/sixtyfps_interpreter.h

@@ -376,6 +376,7 @@ public:
     }
 
 private:
+    inline Value(const void *) = delete; // Avoid that for example Value("foo") turns to Value(bool)
     using ValueOpaque = sixtyfps::cbindgen_private::ValueOpaque;
     ValueOpaque inner;
     friend struct Struct;