[enhancement] New message storing data points in EstimatorModel

[hnpl]

What's hard to do? (limit 100 words)

Currently, message EstimatorModel uses message DataPoint to store data points for an estimator model. While an estimator model is supposed to estimate exactly one metric, message DataPoint retains all information from synthesis, such as area and delay for an op.

Current best alternative workaround (limit 100 words)

N/A

Your view of the "best case XLS enhancement" (limit 100 words)

We should add another message recording value and value_offset of one metric instead of reusing message DataPoint in message EstimatorModel.