Consider moving PassFactory instances into static fields on the passes themselves

Currently the bottom 2/3 of `DefaultPassConfig` is a bunch of `PassFactory` instances. Previously these were very trivial, but they are getting more significant now that things like `featureSet` or `transpiledFeatures` are getting added.

To keep them better in-sync with the actual passes, it seems to make sense to move the factories to the passes themselves. So for instance, we would write

```java
class CheckRequires implements HotSwapCompilerPass {
// ...
static final HotSwapPassFactory FACTORY =
new HotSwapPassFactory("checkMissingAndExtraRequires") {
// ...
};
}
```
and then in `DefaultPassConfig` it would just be
```java
checks.add(CheckRequires.FACTORY);
```

Is there a reason we shouldn't do this?