[WIP] Fix TFVC check-in changes not working after upgrade to VS2026

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>TFVC - Check-in changes doesn't work after upgrade to VS2026</issue_title>
<issue_description>TFVC - Check-in changes doesn't work after upgrade to VS2026.

Error: Cannot convert the "Microsoft.TeamFoundation.Client.TfsClientCredentials" value of type "System.String" to type "System.Type".
TfsClientCredentials was deprecated in Microsoft.TeamFoundation.Client.dll 16.0 and it doesn't work with Microsoft.TeamFoundation.Client.dll 20.0 at all.</issue_description>

Comments on the Issue (you are @copilot in this section)

@jessehouwing My bandwidth to fix this is currently low and I personally do not have any clients that use this feature anymore as far as I am aware. I suspect the required changes are limited, I'd appreciate a PR in case anyone has the time to debug. @jessehouwing Possible solution avenues:

1. Download the nuget for client I object model 16 and commit it to the task folder.
2. Remove latest from the call to vswhere and offer a dropdown with specific versions or provide a version range.
3. Use load the assembly using reflection, read it's version number and adjust the loflgic depending on the version found.

• Fixes TFVC - Check-in changes doesn't work after upgrade to VS2026 #118

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[jessehouwing]

@copilot report, why did you assign back to me?