[wgsl-in] Parse error for subtraction in array index

This shader:
```rust
var<workgroup> a: array<u32, 64>;

fn foo() {
    let x = 1;
    let y = a[x-1];
}
```
Produces this error:

```
error: expected ']', found '-1'
  ┌─ a.wgsl:6:16
  │
6 │     let y = a[x-1];
  │                ^^ expected ']'

Could not parse WGSL
```
