Provide API to get MT/EEClass/MD for Desktop flavor

[zvirja]

Extend ClrMD API and allow to access the following data.

For ClrType:

• MethodTable address;
• EEClass address.

Ensure that EEClass data is correct for generics (which could share the same MT, AFAIK).

For the ClrMethod:

• MethodDesc address.

[leculver]

I have added basic support for getting raw runtime pointers (MethodTable, EEClass, MethodDesc). I need to spend some time writing documentation on it, but I'm not sure when I'll have time for it. I've implemented enough I'm going to go ahead and close this issue, but there's two outstanding issues:

1. I need to make sure there's nothing I missed with EEClass. I will talk to an expert on the team tomorrow.
2. While the basic functionality is implemented, I did not cache a lot of the calculations that need to be done. If you are using EnumerateMethodTables or EnumerateMethodDescs on a multiple-AppDomain targets, you will likely see very bad performance until I can find the right performance tradeoff.

(Specifically on 2, we will hit GetMethodTableList and enumerate through them when looking for a particular type's MethodTables. If you start seeing bad perf in those methods, the uses of that function is the place to start digging.)