Port System.Numerics docs for .NET 9 APIs #105981
Description
Below is the list of APIs that still show up as undocumented in dotnet-api-docs and were introduced in .NET 9.
Full porting instructions can be found in the main issue.
This task needs to be finished the day before the RC2 snap (September 15th).
Undoc APIs for RC1 as of 2024/10/01: #105981 (comment)