[mlir] Expose a mechanism to provide a callback for encoding types and attributes in MLIR bytecode.
Two callbacks are exposed, respectively, to the BytecodeWriterConfig and to the ParserConfig. At bytecode parsing/printing, clients have the ability to specify a callback to be used to optionally read/write the encoding. On failure, fallback path will execute the default parsers and printers for the dialect.
Testing shows how to leverage this functionality to support back-deployment and backward-compatibility usecases when roundtripping to bytecode a client dialect with type/attributes dependencies on upstream.
Reviewed By: rriddle
Differential Revision: https://reviews.llvm.org/D153383
bff6a4292f