`#ctor` in see crefs needs to be converted to `%23ctor`

[carlossanlop]

Otherwise it causes build failures in the dotnet-api-docs CI.

Examples:
https://github.com/dotnet/dotnet-api-docs/pull/7889/files#r837782607
https://github.com/dotnet/dotnet-api-docs/pull/7889/files#r837782386