[mlir][PDL] Add support for variadic operands and results in PDL

This revision extends the PDL dialect to add support for variadic operands and results, with ranges of these values represented via the recently added !pdl.range type. To support this extension, three new operations have been added that closely match the single variant:
* pdl.operands : Define a range of input operands.
* pdl.results : Extract a result group from an operation.
* pdl.types : Define a handle to a range of types.

Support for these in the pdl interpreter dialect and byte code will be added in followup revisions.

Differential Revision: https://reviews.llvm.org/D95721