Add SystemCondition-satisfying closure "resource_exists_and"

## What problem does this solve or what need does it fill?

Bevy has [three similar functions](https://docs.rs/bevy/latest/bevy/?search=resource_exists):
- `resource_exists`
- `resource_exists_and_changed`
- `resource_exists_and_equals`

## What solution would you like?

Add another system `resource_exists_and` which takes a more arbitrary condition, e.g.
```rust
struct CombatQueue>;
update_new_combat_ui.run_if(resource_exists_and(|queue: &CombatQueue| queue.0.is_empty()))
```

## What alternative(s) have you considered?

I suppose there's other ways of doing very similar things (e.g. you could make a new State and have systems condition on them, then make a system in PostUpdate or PreUpdate to update said State depending on the condition of the Resource) but I think this is convenient and reduces the lines of code needed a lot, especially for one-off and simple condition checks where such a State would just be tracking a Resource anyway.

## Additional context

I've implemented this for my personal usage as follows, by copying+modifying the `resource_exists_and_equals` system:
```rust
pub fn resource_exists_and(condition: impl Fn(&T) -> bool) -> impl FnMut(Option>) -> bool
where
T: Resource,
{
move |res: Option>| match res {
Some(res) => condition(&res),
None => false,
}
}
```
It's working well for me so far.

Locate the existing `resource_exists`, `resource_exists_and_changed`, and `resource_exists_and_equals` implementations and their related tests. Add the requested `resource_exists_and` condition with the demonstrated predicate behavior, including returning false when the resource is absent, then run the relevant tests.

Written by the indexing model from the issue text.