* Run validator during reduction.
* Added functionality to validate modules after each reduction step, and some tests to check this is working. Also fixed an issue where reduction passes were not guaranteed to be executed at their minimum granularities.
Add a spirv-reduce pass which removes OpName and OpMemberName instructions.
This is useful to enable other reduction passes, e.g. RemoveUnreferencedInstruction may not be able to remove an instruction creating an id whose only usage is an OpName for this id.
