[delegate-virtual-trampoline] Add virtual parameter to existing JIT time code path
[delegate-virtual-trampoline] Add virtual functions delegate trampoline support

This optimization is activated in the ldvirtftn + delegate case, and is deactivated in the case where the architecture does not support it (mono_arch_get_delegate_virtual_invoke_impl return NULL)
Merge pull request #1161 from ludovic-henry/pr22-delegate-virtual-trampoline

[delegate virtual] Improve trampoline caching