Add polyfills for .NET 10 attributes.

[teo-tsirpanis]

Note

Depends on #127.

API breakdown (for new features)

Polyfills for the following attributes were added:

• [CompilerLoweringPreserve]
  • Also applied to the polyfill for DynamicallyAccessedMembersAttribute, matching upstream.
• [ExtensionMarker]
• The DynamicDependencyAttrribute.Condition property in the polyfill was obsoleted and hidden, matching upstream.

Polyfills for the following runtime-supported attributes were added:

• [UnsafeAccessorType]

Additional context (optional)

The list of attributes was populated by searching for the regex : .+Attribute in files matching release-notes/10.0/api-diff/Microsoft.NETCore.App in the branch of dotnet/core#10147, and excluding the attributes in OOB packages.

.NET 10 added the following properties to existing attributes that we polyfill:

namespace System.Diagnostics.CodeAnalysis
{
    public sealed class ExperimentalAttribute : System.Attribute
    {
+       public string? Message { get; set; }
    }
    public sealed class RequiresDynamicCodeAttribute : System.Attribute
    {
+       public bool ExcludeStatics { get; set; }
    }
    public sealed class RequiresUnreferencedCodeAttribute : System.Attribute
    {
+       public bool ExcludeStatics { get; set; }
    }
}

Because it would lead to an inconsistent experience, where the polyfills will be added when targeting say .NET Standard, but not a .NET version earlier than 10, these changes are not polyfilled at this moment.

Also, the following runtime-supported attributes were not polyfilled:

• TypeMapAssemblyTargetAttribute<TTypeGroup>, TypeMapAssociationAttribute<TTypeGroup>, and TypeMapAttribute<TTypeGroup>, because they are generic and would cause issues on downlevel runtimes.
• MetadataUpdateDeletedAttribute, because it is emitted by Hot Reload, and applying it manually is not allowed.

[teo-tsirpanis]

PR description updated for .NET 10 RTM's release; no new useful attributes were added since. This is ready for review.