[mlir:Bytecode] Add support for encoding resources

Resources are encoded in two separate sections similarly to
attributes/types, one for the actual data and one for the data
offsets. Unlike other sections, the resource sections are optional
given that in many cases they won't be present. For testing,
bytecode serialization is added for DenseResourceElementsAttr.

Differential Revision: https://reviews.llvm.org/D132729