dotnet: emit features for ldftn/ldvirftn instructions

[mike-hunhoff]

• ldftn: https://docs.microsoft.com/en-us/dotnet/api/system.reflection.emit.opcodes.ldftn?view=net-6.0
• ldvirftn: https://docs.microsoft.com/en-us/dotnet/api/system.reflection.emit.opcodes.ldvirtftn?view=net-6.0

e.g.

... ldftn     instance void malware.methods::timer_callback(object)
... newobj    instance void [mscorlib]System.Threading.TimerCallback::.ctor(object, native int)

emit

- namespace: malware
- class: malware.methods
- function-name: malware.methods::timer_callback