Extend E0623 for fn and trait objects WIP

[gaurikholkar-zz]

Examples

fn foo<'a,'b>(x:  for<'c, 'd> fn(&'c u8, &'d u8), y: Vec<&'a u8>, z: &'b u8) {
  y.push(z); // index will be zero or one
}

cc @nikomatsakis @estebank @arielb1 @GuillaumeGomez

[gaurikholkar-zz]

An extension of #43269

[gaurikholkar-zz]

Made basic changes in this commit.
Gives me the following error
Edit: fixed

[gaurikholkar-zz]

This has been taken care in #44516

[estebank]

Closing as per #44516.