Preserve type converters for aot/trimmer

[maxkatz6]

This PR fixes several warnigns/erros that are reproducible during PublishAOT build with Svg.Skia library referenced:

    /_/externals/SVG/Source/DataTypes/SvgAspectRatio.cs(59): Trim analysis error IL2026: Svg.SvgAspectRatio.ToString(): Using member 'System.ComponentModel.TypeDescriptor.GetConverter(Type)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Generic TypeConverters may require the generic types to be annotated. For example, NullableConverter requires the underlying type to be DynamicallyAccessedMembers All.
    /_/externals/SVG/Source/DataTypes/SvgAspectRatio.cs(59): AOT analysis error IL3050: Svg.SvgAspectRatio.ToString(): Using member 'System.Enum.GetValues(Type)' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. It might not be possible to create an array of the enum type at runtime. Use the GetValues<TEnum> overload or the GetValuesAsUnderlyingType method instead.

These special attributes fix the problem by ensuring attributes are statically linked, and not removed from the assembly. Without changing any logic.

[wieslawsoltes]

@maxkatz6 This need to go the upstream repository https://github.com/svg-net/SVG