Auto merge of #150309 - dianqk:ssa-range, r=cjgillot

New MIR Pass: SsaRangePropagation

As an alternative to rust-lang/rust#150192.

Introduces a new pass that propagates the known ranges of SSA locals.
We can know the ranges of SSA locals at some locations for the following code:
```rust
fn foo(a: u32) {
  let b = a < 9;
  if b {
    let c = b; // c is true since b is whitin the range [1, 2)
    let d = a < 8; // d is true since b whitin the range [0, 9)
  }
}
```

This PR only implements a trivial range: we know one value on switch, assert, and assume.

Author: bors