Replace deprecated SecTrustGetCertificateAtIndex API in System.Security.Cryptography.Native.Apple

[akoeplinger]

When bumping to macOS12/iOS12.2 in #101342 we got a new warning about this API being deprecated.

From @filipnavara

The SecTrustGetCertificateAtIndex deprecation would need a new code path to use SecTrustCopyCertificateChain. To make that efficient we would likely need to rewrite the managed -> native interface.

[dotnet-policy-service]

Tagging subscribers to 'os-ios': @steveisok, @akoeplinger, @kotlarmilos
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to 'os-tvos': @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to 'os-maccatalyst': @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-security, @bartonjs, @vcsjones
See info in area-owners.md if you want to be subscribed.

[vcsjones]

As noted in #101342 (comment), I have a head start on deprecation replacements so I can just include this one in the work.

[vcsjones]

Bumping this to 10.0, it's not blocking for 9.0.