Auto merge of #30707 - tsion:mir-text, r=nikomatsakis
r? @nikomatsakis
Textual MIR can be dumped for a particular `fn` with `#![rustc_mir(pretty = "filename.mir")]`. Below is an example of the text output.
```rust
struct Point {
x: i32,
y: i32,
}
fn example() -> Point {
let mut e = Point { x: 1, y: 2 };
let num = 5;
let plus_num = |x: i32| x + num;
e.y = plus_num(e.x);
e
}
```
```rust
fn() -> Point {
let mut var0: Point; // e
let var1: i32; // num
let var2: [closure@test.rs:84:20: 84:36 num:&i32]; // plus_num
let mut tmp0: ();
let mut tmp1: &i32;
let mut tmp2: ();
let mut tmp3: i32;
let mut tmp4: &[closure@test.rs:84:20: 84:36 num:&i32];
let mut tmp5: i32;
let mut tmp6: Point;