IR Arguments/ArgumentValue should support Float16.

Currently if you do:

```
  @Arguments(values = {Argument.NUMBER_42, Argument.NUMBER_42})
  public Float16 test_10(Float16 a, Float16 b) {
     ...
  }
```

You get:

```
 - Provided invalid NUMBER_42 argument for non-number jdk.incubator.vector.Float16 arg0 for public jdk.incubator.vector.Float16 compiler.igvn.templated.MinMaxIdentity.test_10(jdk.incubator.vector.Float16,jdk.incubator.vector.Float16)
```

It should be possible to create Float16 constants for 42/-42 and create randoms.