[cdac] Implement ExecutionManager.ReadyToRunJitManager.GetMethodInfo (minus handling of hot/cold lookup)

[elinor-fung]

Implement ExecutionManager.ReadyToRunJitManager.GetMethodInfo without handling of hot/cold lookup. This maps to ReadyToRunJitManager::JitCodeToMethodInfo in the runtime. Basic logic is:

• Check if the address is in a thunk for READYTORUN_HELPER_DelayLoad_MethodCall
• Find the runtime function entry corresponding to the address
• Look up the MethodDesc for the entry point using the ReadyToRunInfo's hash map

Add tests for ExecutionManager for getting code blocks and method desc in R2R and for HashMap lookup functionality

• Start using Moq - this change only uses it to mock IPlatformMetadata, but I think we should be able to use this instead some of the explicit subclasses we have for testing.
• Simplify usage of TestPlaceholderTarget such that setting the reader delegate and data cache are not explicit operations - make its constructor take a reader delegate and always create a default data cache
• Slight clean up of ExecutionManagerTestBuilder - make it more consistent with MockDescriptors.*
  • I think this should probably also be moved under MockDescriptors, but I didn't want to do that in this change (same with some helpers in other test classes, like PrecodeStubsTests)

Manually validated with !clrstack and !ip2md in windbg that R2R functions now show up correctly (were <unknown> before this change).

Contributes to #99302, #109426

[dotnet-policy-service]

Tagging subscribers to this area: @tommcdon
See info in area-owners.md if you want to be subscribed.