[mlir] ODS: support operations with resizable operand lists

MLIR supports operations with resizable operand lists, but this property must
be indicated during the construction of such operations. It can be done
programmatically by calling a function on OperationState. Introduce an
ODS-internal trait `ResizableOperandList` to indicate such operations are use
it when generating the bodies of various `build` functions as well as the
`parse` function when the declarative assembly format is used.

Differential Revision: https://reviews.llvm.org/D78292