The previous implementation could emit 'wildcard' channel layouts in too
many scenarios.
A wildcard channel count is -1 or -2, and indicates that any number of
channels is supported on the bus.
If the input and output layouts must match, then a layout of [-1, -1]
should be returned.
If any layout is valid in both directions, then a layout of [-1, -2]
should be returned.
In the case where we have a bus A and opposite bus B, we will now only
emit a wildcard count for bus A if every bus standard bus layout up to a
channel count of 16 can be applied successfully without changing the bus
count of B.
To prevent too much disruption to people who have our public projects as
part of their build or testing systems we are temporarily ignoring a
warning about using Xcode 15.
