Properly handle const if expression when using proc-scoped channels

[magancarz]

This PR adds handling proper branch from const if when converting DSLX to IR with lower_to_proc_scoped_channels flag enabled. While it works on added ConstConditionalProcScoped test case, it breaks when trying to get a constexpr value from the test expression if const if is inside a parametric proc with the following error:

Error: NOT_FOUND: No constexpr value found for node `CONFIG` (NameRef) @ xls/examples/const_if.x:47:18-47:24

This issue can be reproduced by trying to build the const_if_ir example with changes from this PR.

[magancarz]

I've included a fix for using the correct type info when traversing parametrized proc's hierarchy in get_conversion_records.cc with proc-scoped channels enabled. It is based on deferring the traversal in HandleProc for parametric procs, so that the type info objects for config and next functions are later retrieved from spawn data and from resolved_proc_alias in case of top parametric procedures.
FYI @dplassgit