Add lint: &mut Commands function argument

[BD103]

Quoting @ItsDoot in bevyengine/bevy#15657:

How can Bevy's documentation be improved?

We should more clearly and directly recommend that developers write their helper functions to take Commands (and friends) directly, instead of passing as references (&Commands). And by doing so, these helpers can look just like systems. As an example:

fn my_system(commands: Commands, foo: Query<&Foo>) {
    // we should recommend this:
    good_helper(commands.reborrow(), foo.reborrow());
    // instead of this:
    bad_helper(&mut commands, &foo);
}

// This is kind of annoying:
fn bad_helper(commands: &mut Commands, foo: &Query<&Foo>) {
    // ...
}

// This is easier to deal with:
fn good_helper(commands: Commands, foo: Query<&Foo>) {
    // ...
}

We should recommend reborrowing in the top level docs for Commands and Query.

We can write a lint that would warn against taking &mut Commands in a function! It would probably be in the pedantic category, though.

[janhohenheim]

TIL about reborrow 👀