Document System.Text.RegularExpressions.GroupCollection

[carlossanlop]

This one was interesting because the class implements IList and ICollection, which have shared method names.
Strangely, there were a couple of members that were duplicate, so I removed them. Please let me know if it was wrong to do so.

Here is the code: GroupCollection.cs

I based the documentation on the interface comments:

• ICollection: https://docs.microsoft.com/en-us/dotnet/api/system.collections.icollection?view=netcore-3.0
• IList: https://docs.microsoft.com/en-us/dotnet/api/system.collections.ilist?view=netcore-3.0

Area owners: @ViktorHofer, @maryamariyan
Language review: @rpetrusha, @Jemash

[rpetrusha]

I've left a number of comments and suggestions, @carlossanlop. Most importantly, the members that you removed should be restored, since they evidently were supported in .NET Core 1.0 and 1.1.

[carlossanlop]

I addressed your comments, @rpetrusha. I had to to a git push -f so the previous commits are not showing up anymore, but I merged all your rewording suggestions, the EIIs and the "not supported" changed messages.

[rpetrusha]

This looks good, @carlossanlop. I thought that there were a few more places where we should add "This is an explicit interface implementation..."

[carlossanlop]

@mairaw @rpetrusha I applied your suggestions Ron, thanks for finding the additional remarks. I modified them a bit to include CDATA, otherwise the xrefs would give us trouble. Let me know if they look good while we wait for the build to finish.

[rpetrusha]

This looks good, @carlossanlop. I just noticed that there's one more EII (ICollection.CopyTo) that could have the "This member is an EII..." text, but I'll open a PR to add it separately, and I'll merge your PR now.