Blender Git Loki

Cycles X: Make pass definition more robust to changes

Previously adding, removing, or even changing order of passes in
the kernel_types.h would likely to break display pass enum.

This was because the python enum was relying on an exact match of
enum item values.

Now we do an identifier-based lookup via `Pass::get_type_enum`,
which allows to more safely change passes in kernel without risk
of breaking display passes.

Additionally, conversion of pass to string now also happens via
the `Pass::get_type_enum`.

All in all, it is the pass type enum which s the source of truth
with this change.

Differential Revision: https://developer.blender.org/D11823