7131: Created an assist for inlining a function's body into its caller r=matklad a=Michael-F-Bryan
This introduces an `inline_function` assist which will convert code like this:
```rust
fn add(a: u32, b: u32) -> u32 { a + b }
fn main() {
let x = add<|>(1, 2);
}
```
Into something like this:
```rust
fn add(a: u32, b: u32) -> u32 { a + b }
fn main() {
let x = {
let a = 1;
let b = 2;
a + b
};
}
```
Fixes#6863.
Co-authored-by: Michael-F-Bryan <michaelfbryan@gmail.com>
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