Clarify interaction between records and varargs

Both of the following are accepted by the current `javac`, but probably should not be:

```
record Test(int[] args) {
  public Test(int... args) {
    this.args = args;
  }
}
```
and

```
record Test(int... args) {
  public Test(int[] args) {
    this.args = args;
  }
}
```

These both probably fall into the "an explicit canonical ctor should match the record descriptor exactly" bucket. There is little benefit to such divergence.