This PR fixes a bug in the selector parser where an attribute selector
followed by a type selector inside a compound selector resulted in the
wrong result.
Given you have this CSS:
```css
[data-foo]div {}
```
Then parsing it before this PR, would result in:
```ts
{
kind: 'compound',
nodes: [
{ kind: 'selector', value: '[data-foo]div' },
],
},
```
But with this PR, it's properly split:
```ts
{
kind: 'compound',
nodes: [
{ kind: 'selector', value: '[data-foo]' },
{ kind: 'selector', value: 'div' },
],
},
```
I also tweaked some of the comments in the parser that are unrelated,
but I was there already.
## Test plan
1. Added a regression test
2. All other tests should pass
67c745efde