Feature request: simplify match expression

When I'm refactoring and inlining stuff all over the place, I often end up with cases like this:

match Some(foo()) {
  None => { do_none() }
  Some(0) => { do_0() }
  Some(1) => { do_1() }
  _ => { do_wild() }
}

I would love an assist that keeps only the Some branches and simplifies this to

match foo() {
  0 => { do_0() }
  1 => { do_1() }
  _ => { do_wild() }
}

It would also make sense for if lets and even plain ifs.

I realize this is unlikely to be actionable until match checking is librarified, but that's not too far in the future hopefully.

Start with the Rust match, if let, and if examples in the issue, then assess the stated prerequisite that match checking be librarified. Done means an assist can simplify the shown Some match while preserving the 0, 1, and wildcard branches, with the intended scope for if let and plain if clarified.