Enable trimming

[twsouthwick]

We want to ensure that the library is compatible with the trimming in .NET 6+. In order to enable this, a few warnings must be addressed. These all appear to be somewhere in the M-L range of effort, generally requiring a bit of a redesign.

• Trimming: ClassActivator{T} usage #1173
• Trimming: ReflectionBasedRootElementFactory #1174
• Trimming: EnumInfoLookup #1175

Ideally, we replace these with non-reflection usage. However, we may be OK with punting that and just getting things annotated so the linker will know what to do.