Collapsing double `if let Some(…)` should also suggest `and_then()`

This is a request to extend the collapsible_if lint to also suggest using the and_then() function for scenarios where two if let Some(…) constructs would be collapsed into one if statement:

fn main() {

	// A double nested datastructure that will be something more complex in real code i.e. a regex capture
	let thingy: Option<Option<u8>> = Some(Some(1));

	if let Some(thing) = thingy {
		if let Some(value) = thing {
			println!("Value: {value}");
		}
	}

	// What clippy suggests
	if let Some(thing) = thingy
		&& let Some(value) = thing {
			println!("Value: {value}");
		}

	// What clippy should (also) suggest when unwrapping two `Option` types
	if let Some(value) = thingy
		.and_then(|thing| thing) {
			println!("Value: {value}");
		}
	
}

Note that in more complex code the placeholders thingy and thing are most likely not options themselves, but some datastructures that have a method called that results in an Option.

This might also be applicable to Results.

This applies to clippy 0.1.92 (54a8a1db60 2025-09-26)

Start with the existing collapsible_if lint referenced in the issue and reproduce the nested Option example. Determine whether the requested and_then() suggestion applies beyond Option, including the noted Result possibility. Done means the lint handles the intended nested cases without changing the existing && let suggestion.