Produce JSON file with TFMs and (at least) their EOL status

[richlander]

We want to present EOL information in NuGet: NuGet/NuGetGallery#9837

However, NuGet has TFMs not .NET versions. There is no straightforward way to map net5.0 to channel-version == 5.0 in https://github.com/dotnet/core/blob/main/release-notes/releases-index.json. Yes, sure, IndexOf the net string. It gets more complicated with TFMs with OS versions in them.

We need a JSON format with the following characteristics:

• TFM
• Is EOL?
• Parent TFM and/or .NET version and/or OS version

Ideally, you can see from this file is an EOL is supported or not and can tell from additional files when the TFM will be EOL based on its parents.

For example, net8.0-ios72 is parented to both .NET 8 and iOS v72. The file should describe that relationship. We shouldn't record when .NET 8 or iOS 72 goes EOL in this file but tell people where else to look for that information, like https://github.com/dotnet/core/blob/main/release-notes/releases-index.json