Add Mac Catalyst NuGet packages and fix iOS NuGet packages

[sungaila]

1. Adds bblanchon.PDFium.MacCatalyst and bblanchon.PDFiumV8.MacCatalyst as NuGet packages.
2. Adds tragetFramework to certain NuGet packages. These are not strictly needed (netstandard1.0 covers almost everything) but makes their target platforms more clear.
3. Fixes iOS NuGet packages with correct runtime identifier (see PortableRuntimeIdentifierGraph.json for all valid RIDs).
4. Updates NuGet copyright to 2025.

Mac Catalyst should be its own NuGet package (see also other popular packages like SkiaSharp.NativeAssets.MacCatalyst).

Putting both iOS device and simulator builds into the same NuGet package is good and should be kept this way.

[bblanchon]

Hi @sungaila,

Thank you very much for this PR.

I merged the changes that are not related to Catalyst in 8492f89, 73c254b, and b9b79fb.

Before merging the Catalyst part, I wanted to discuss with you the possibility of naming this package iOSCatalyst (or simply Catalyst) to be consistent with the rest.
As a reminder, the tarballs are named ios-catalyst because the name is composed of target_os and target_environment, which are imposed by PDFium.

I was also wondering if it would be possible to merge this one with the iOS package, as we did for device and simulator.

Please let me know what you think.

Best regards,
Benoit

[sungaila]

I was also wondering if it would be possible to merge this one with the iOS package, as we did for device and simulator.

Fair enough. From dotnet's point of view, iOS is a superset of Mac Catalyst so putting these binaries into the iOS NuGet package makes sense.

I will update the pull request.

[sungaila]

I've merged the MacCatalyst binaries back into the iOS NuGet package.

Also I fixed a few NuGet pack warnings I noticed while testing. Some missing placeholder files, sometimes using PDFium instead of PDFiumV8 in the file name.