fix broken links

[mairaw]

@JeremyKuhne, @carlossanlop found some broken links while browsing the docs for
https://docs.microsoft.com/en-us/dotnet/api/system.io.memorystream.trygetbuffer?view=netframework-4.8

Also, what about the other constructors? The remarks only list 5 but MemoryStream has at least 7

[carlossanlop]

Thanks for letting me know, Maira. I think I may have introduced those broken links, yet I don't recall seeing build warnings or failures.
I can add the rest of the constructors in a new PR.

[mairaw]

It looks like they're working now so I'll merge this:
https://review.docs.microsoft.com/en-us/dotnet/api/system.io.memorystream.trygetbuffer?view=netframework-4.8&branch=pr-en-us-3663