Add more reflection tests for `Handle` (#24115)

## Objective

Build on #24048 to improve test coverage for `Handle` reflection, and
also repro #24111.

## Solution

Add various tests. Includes a test for valid cases of `from_reflect` and
`try_apply` - this is relevant since `from_reflect` now has a custom
implementation.

I've snuck in a few cleanups too:

- Avoid multiple tests repeating the same imports.
- Fix an accidentally duplicated comment.

## Testing

```sh
cargo test -p bevy_asset
```

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Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>