I'm still on the fence about leaving complex input/output definitions
intact. However, this provides enough support to walk such structures
all the way down to the leaves and determine exactly which components
are in use, what their types are, and what the interpolation qualifiers
etc should be.

Bug: b/120799499

Change-Id: Ia1e46a571126088e29bfdab6bc5ece0343e294e4
Reviewed-on: https://swiftshader-review.googlesource.com/c/23176Tested-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>