Clean up optimize_acqf and _make_linear_constraints (meta-pytorch#1660)

Summary:
Pull Request resolved: meta-pytorch#1660

Bot was rightly complaining about complexity
- pulled out method to validate inputs for `_make_linear_constraints`
- introduced a dataclass to contain and validate the inputs for `optimize_acqf`
- `optimize_acqf` now calls one of three different `optimize_acqf_[name]` functions

Reviewed By: Balandat

Differential Revision: D43012356

fbshipit-source-id: cad97932e5574b2cc9de8e912d9da9ab1dd22f1f

Author: esantorella