Suggested Error Prone pattern: NumberFormatContstant (like existing DateFormatConstant)

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### Description of the problem / feature request:

The existing pattern for DateFormatConstant (along with its fix, adding a ThreadLocal initializer) should be adapted to also support NumberFormat and DecimalFormat. There may also be other common thread-unsafe Format classes that would make sense to treat similarly.

### Feature requests: what underlying problem are you trying to solve with this feature?

Similar to DateFormat, NumberFormat is not threadsafe.

### Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.
```java
class Foo {
public static NumberFormat FORMAT = NumberFormat.getInstance()
// call FORMAT.format() from multiple threads concurrently and wait for things to go wrong
}
```

### What version of Error Prone are you using?

2.3.3

### Have you found anything relevant by searching the web?

Here's a discussion on the java bugtracker https://bugs.java.com/bugdatabase/view_bug.do?bug_id=4101500