make operations provide a list of canonicalizations that can be applied to
them. This allows canonicalization to be general to any IR definition.
As part of this, sink PatternMatch.h/cpp down to the IR library to fix a
layering problem.
PiperOrigin-RevId: 218773981
This is done by changing Attribute to be a POD interface around an underlying pointer storage and adding in-class support for isa/dyn_cast/cast.
PiperOrigin-RevId: 218764173
just having the pattern matcher in its own library. At this point,
lib/Transforms/*.cpp are all actually passes themselves (and will probably
eventually be themselves move to a new subdirectory as we accrete more).
PiperOrigin-RevId: 218745193
