[mlir:python] Compute get_op_result_or_value in PyOpView's constructor.

This logic is in the critical path for constructing an operation from
Python. It is faster to compute this in C++ than it is in Python, and it is a
minor change to do this.

This change also alters the API contract of
_ods_common.get_op_results_or_values to avoid calling
get_op_result_or_value on each element of a sequence, since the C++ code
will now do this.

Most of the diff here is simply reordering the code in IRCore.cpp.

Author: hawkinsp