Failed reformatting on simultaneous declarations

Hi there,

I meet a problem when trying to use google-java-format to re-format on simultaneous declarations in a java file:

According to Google Java Style Guide [4.8.2-variable-declarations](https://google.github.io/styleguide/javaguide.html#s4.8.2-variable-declarations):

>Every variable declaration (field or local) declares only one variable: declarations such as `int a, b;` are not used.

However, given java file:

```java
public class ReplaceColor {
private int oldRed, oldGreen, oldBlue;
private IntRange oldRedRange, oldGreenRange, oldBlueRange;
private boolean isRange;
}
```

using google-java-format would not re-format the simultaneous declarations in above file.

Is this a defect that google-java-format forget to consider about?

If not, could you guys help me a bit on pointing out where should I getting started to hack this project to get this feature in my own fork?

Many thanks & best wishes,

Charles

Start by reviewing google-java-format's handling of Java variable declarations and the Google Java Style Guide section 4.8.2 cited in the issue. Reproduce the sample with simultaneous declarations, then add coverage for the expected reformatted output; done means each declaration is formatted separately or the behavior is documented as intentional.

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