Cannot derive `Reflect` on a struct with `Option<Box<T>>` field where `T: Reflect`

## Bevy version

v0.12

## What you did

```rust
#[derive(Reflect)]
pub struct Foo {
pub problem: Option>,
}
```

## What went wrong

```
error[E0277]: the trait bound `std::boxed::Box: TypePath` is not satisfied
--> src/bug.rs:5:18
|
25 | pub problem: Option>,
| ^^^^^^^^^^^^^^ the trait `TypePath` is not implemented for `std::boxed::Box`
|
```

## Additional information

This was compiling on v0.11.

Reproduce the generic #[derive(Reflect)] example on Bevy v0.12 and inspect the Reflect derive and TypePath handling for Option>. Compare the behavior with v0.11; done means the example compiles again for T: Reflect without the Box: TypePath error.

Written by the indexing model from the issue text.