Implement TrialResult.__eq__ using pandas.DataFrame.equals (#1810)
Implement TrialResult.__eq__ using pandas.DataFrame.equals (#1810)

- Can't use _value_equality_values_ because pandas.DataFrame.__eq__ broadcasts instead of returning a bool
- This is much more efficient than using the repr

I believe the test failures are due to having series within the table. So blocked by https://github.com/quantumlib/Cirq/pull/1811
quantumlib/Cirq,quantumlib/Cirq,balopat/Cirq,balopat/Cirq,quantumlib/Cirq,quantumlib/Cirq,balopat/Cirq,quantumlib/Cirq