Add deprecation note to CustomBuildEventArgs #9220
Description
Extracted from dotnet/docs#36403:
https://learn.microsoft.com/en-us/dotnet/api/microsoft.build.framework.custombuildeventargs?view=msbuild-17-netcore needs to link to https://learn.microsoft.com/en-us/dotnet/core/compatibility/sdk/8.0/custombuildeventargs.
CustomBuildEventArgs is deprecated; use ExtendedCustomBuildEventArgs instead.
Assign to @ghogen