[mlir] Expose output strategies of TimingManager (#166548)
After the original API change to DefaultTimingManager::setOutput() (see
362aa434cc31ccca96749a6db8cd97f5b7d71206), users are forced to provide
their own implementation of OutputStrategy. However, default MLIR
implementations are usually sufficient. Expose Text and Json strategies
via factory-like method to avoid the problem in downstream projects.
