New assist: move_format_string_arg
The name might need some improving.
```rust
fn main() {
print!("{x + 1}");
}
```
to
```rust
fn main() {
print!("{}"$0, x + 1);
}
```
fixes#13180
ref to #5988 for similar work
* extracted `format_like`'s parser to it's own module in `ide-db`
* reworked the parser's API to be more direct
* added assist to extract expressions in format args
f64c95600c