Added coreclr_unity profiler api for getting AssemblyLoadContext information

[alexey-zakharov]

To detect AssemblyLoadContext leaks which are coming from static fields we need to be able to:

1. Connect AsemblyLoadContext to LoaderAllocator instance which holds a special array (m_slots) with statics and other AssemblyLoadContext-specific roots.
2. Quickly determine which AssemblyLoadContext specific class belongs to. (An ALC of a generic instance depends on ALCs of type parameters and is relatively expensive to compute)

Unfortunately there is no link in managed for both cases (AssemblyLoadContext and LoaderAllocator can't know about each other to be able to actually unload ALC). However in native there is an AssemblyBinder class which knows about both objects through a native handle, and can directly point to the ALC for a given class.

The PR introduces:

1. coreclr_unity_profiler_assembly_load_context_get_loader_allocator_handle - api to retrieve LoaderAllocator handle for an AssemblyLoadContext instance.
2. coreclr_unity_profiler_class_get_assembly_load_context_handle - api to return AssemblyLoadContext handle for a class instance.

It may be possible to suggest a public API to upstream in the future to support this information