System.Data 1.x undocumented APIs

[David-Engel]

Summary

Takes care of some undocumented APIs owned by System.Data.Common and System.Data.SqlClient. that were all introduced in 1.x.

Fixes #3910

[David-Engel]

Not sure why the CI is not providing a review links, but here are a couple starters:
https://review.docs.microsoft.com/en-us/dotnet/api/system.data.common.dbcommand.dispose?view=netcore-1.1&branch=pr-en-us-4233
https://review.docs.microsoft.com/en-us/dotnet/api/system.data.sqlclient.sqlbulkcopycolumnmappingcollection.count?view=netcore-1.1&branch=pr-en-us-4233

[carlossanlop]

Thank you @David-Engel for the PR. The changes look good.
Do any of these APIs throw exceptions? If yes, can you please add them? The xml items for exceptions have to be manually added below the remarks item, like this:

    <remarks>To be added.</remarks>
    <exception cref="T:System.WhateverException">The reason why the exception is thrown.</exception>

[David-Engel]

@carlossanlop

Do any of these APIs throw exceptions? If yes, can you please add them?

Added.

[ajcvickers]

Thanks @David-Engel!

[David-Engel]

@carlossanlop Anything else needed before merging this PR?

Thanks,
David

[BillWagner]

Thanks for all the updates here @David-Engel

I'll now.