[mlir][ODS] Rename several uses of 'description' to 'summary'

Right now constraint/predicate traits/etc. use their "description" field as a one line human readable string. This breaks the current convention, by which a "description" may be multi-line. This revision renames the "description" field in these cases to "summary" which matches what the string is actually used as. This also unbreaks the use of TypeDefs(and eventually AttrDefs) in conjunction with existing type constraint facilities like `Optional`.

Differential Revision: https://reviews.llvm.org/D94133