(1/2) Combine Pauli measurements and postselection (#7746)

I split this #7492 giant PR into
smaller pieces for easier review.
This PR:
1. Adds a CircuitToPauliStringsParameters class which supports
postselection_symmetries.
2. Modify the validation method
3. Allows measure_pauli_strings to take CircuitToPauliStringsParameters
as a input.

Author: ddddddanni

cirq-core/cirq/contrib/paulistring/__init__.py

@@ -45,4 +45,5 @@
 
 from cirq.contrib.paulistring.pauli_string_measurement_with_readout_mitigation import (
     measure_pauli_strings as measure_pauli_strings,
+    CircuitToPauliStringsParameters as CircuitToPauliStringsParameters,
 )