Add Xamarin.Mac.NET (xamarinmacnet)

[joelverhagen]

Address NuGet/Home#2662

• Add xamarinmacnet TFM.
• xamarinmacnet supports net45, xamarinmac, dotnet5.6, and netstandard1.6.
• xamarinmacnet prefers xamarinmac over net45 when both are available.

@emgarten @rrelyea @yishaigalatzer @chamons @mteper @ericstj

[emgarten]

[joelverhagen]

Hey @ghuntley, before making this change, I'd like to understand the scenario a little more. I have some additional questions on the issue:
NuGet/Home#2662

[emgarten]

🔔 Does this still need to go in or should it be closed?

[ghuntley]

Still blocked by NuGet/Home#2662

[ghuntley]

Paging @mhutch as per her comments at NuGet/Home#2662 (comment)

[emgarten]

@joelverhagen any updates on this?

//cc @mishra14

[joelverhagen]

@rrelyea is going to working with someone on client team to push this through. See NuGet/Home#2662 (comment).

[mishra14]

Closing this PR as there has been no traction from the Xamarin folks. This can be reopened, if needed.

[chamons]

@rrelyea @joelverhagen @mishra14 What work on the Xamarin side needs to be done? To our knowledge, it got handed off via:

@rrelyea is going to working with someone on client team to push this through. See NuGet/Home#2662 (comment).

[chamons]

Please consider reopening, this is not fixed or forgotten.

[emgarten]

@chamons will you open a new PR and bring this up to date?

I'm still unclear on the hold up here, but the codebased has changed in 1.5 years and this change likely needs some work to sync it up.

[mrward]

I am planning to resurrect this fix and rebase it on the latest code, just not had chance to look at it yet.

[joelverhagen]

Hey @mrward, is this visible to you?
https://github.com/NuGet/NuGet.Client/pull/562/files

[mrward]

@joelverhagen - Yeah I can see the files from the pull request. I saw the branch was deleted so I thought the changes were gone but they are still available 👍

[joelverhagen]

I've restored the branch -- hope it helps.

[mattleibow]

Reopened this with #2572