add template_value to prelude (#23669)

# Objective

`template_value` is not in the prelude, but seems useful enough to be.
It seems like the main way to include an existing component value in a
`bsn!` declaration since using `{transform}` and similar expressions
doesn't work.

```rust
// some Transform, maybe from an `In<Transform>` or other argument.
let transform = Transform::from_xyz(5., 0., 5.);

bsn! {
    #SomeThing
    template_value(transform)
}
```

## Solution

Add `template_value` to the prelude.