[mlir][OpAsmParser] Add support for parsing integer literals without going through IntegerAttr

Some operations use integer literals as part of their custom format that don't necessarily map to an internal IntegerAttr. This revision exposes the same `parseInteger` functions as the DialectAsmParser to allow for these operations to parse integer literals without incurring the otherwise unnecessary roundtrip through IntegerAttr.

Differential Revision: https://reviews.llvm.org/D93152