Remove Reflection in TrustedRootsHelper

In #16049 we added support for signature verification on Linux. This involved bringing 2 .pem files from the SDK into our aspire-managed.exe.

In order to get NuGet to use these .pem files, we needed to resort to reflecting on internals of NuGet.

Once there is a NuGet version with [Aot compatible: NuGet.Packaging (NuGet/NuGet.Client#7197)](https://github.com/NuGet/NuGet.Client/pull/7197) fixed, we can remove this reflection and instead write the files to a folder named `trustedroots` next to our executable and NuGet will pick up the .pem files without needing for reflection.

This issue is tracking making that change once the available fixes are available.