Math.Atan2(double,double) documentation incorrect for infinite values

### Type of issue

Outdated article

### Description

The documentation for .NET 9.0 is the same as the documentation for .NET Framework 4.8.1. In particular, the lines:

> If x or y is NaN, or if x and y are either PositiveInfinity or NegativeInfinity, the method returns NaN.

This is correct for .NET Framework 4.8.1, but infinite values do not return double.NaN in .NET 9.0 at least:

| y | x | .NET Framework 4.8.1 | .NET 9.0 |
| :-: | :-: | :-: | :-: |
| double.NegativeInfinity | double.NegativeInfinity | double.NaN | - 3π / 4 |
| double.NegativeInfinity | double.PositiveInfinity | double.NaN | - π / 4 |
| double.PositiveInfinity | double.NegativeInfinity | double.NaN | 3π / 4 |
| double.PositiveInfinity | double.PositiveInfinity | double.NaN | π / 4 |

### Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.math.atan2?view=net-9.0

### Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System/Math.xml

### Document Version Independent Id

461d1d25-e500-02fd-3951-69d1e3ca8f0c

### Platform Id

8e8eb576-f9c1-a5ab-514a-735884295c05

### Article author

@dotnet-bot