[ORC] Pass JITDispatchHandler argument buffers as WrapperFunctionBuffer. (#173334)
Updates ExecutionSession::runJITDispatchHandler to take the argument
buffer for the function as a WrapperFunctionBuffer, rather than an
ArrayRef<char>.
This is a first step towards more efficient jit-dispatch handler calls:
1. Handlers can now be run as tasks, since they own their argument
buffer (so there's no risk of it being deallocated before they're run)
2. In in-process JIT setups, this will allow argument buffers to be
passed in directly from the ORC runtime, rather than having to copy the
buffer.