[FEATURE-REQUEST] [BUG] Return and reachable statement

[simonegazza]

Description
Currently, when we are parsing the code, unreachable statement are considered a hard errors and LiSA throws an exception.

Reproducibility information
A programma like the following can produce the error:

fn func() -> i32 {
	let x = 2;
	if x == 2 {
		return 1;
	} else {
		return 3;
	}
	
	return 4;
}

Expected behavior
We should remove the unreachable statements during parsing, or make sure in some ways that LiSA does not give a ProgramValidationException: Unreachable node that is not marked as entrypoint.