Speed up random circuit creation (Qiskit#3249)

The qiskit.circuit.random.random_circuit() function was previously using
signature inspection to figure out how many angles a gate needed. While
this is fine for smaller circuit creation, when the circuits get really
large the time it takes the inspect module to return the signature
starts to add up. The use of the signature check isn't required because
the number of parameters for gates are fixed. This commit speeds random
circuit creation by creating a list of each gate with parameters and
just checking if the randomly selected operation is present in one of
those.

qiskit/circuit/random/utils.py

@@ -14,7 +14,6 @@
 
 """Utility functions for generating random circuits."""
 
-from inspect import signature
 import numpy as np
 
 from qiskit.circuit import QuantumRegister, ClassicalRegister, QuantumCircuit
@@ -52,6 +51,9 @@ def random_circuit(n_qubits, depth, max_operands=3, measure=False,
 
     one_q_ops = [IdGate, U1Gate, U2Gate, U3Gate, XGate, YGate, ZGate,
                  HGate, SGate, SdgGate, TGate, TdgGate, RXGate, RYGate, RZGate]
+    one_param = [U1Gate, RXGate, RYGate, RZGate, RZZGate, Cu1Gate, CrzGate]
+    two_param = [U2Gate]
+    three_param = [U3Gate, Cu3Gate]
     two_q_ops = [CnotGate, CyGate, CzGate, CHGate, CrzGate,
                  Cu1Gate, Cu3Gate, SwapGate, RZZGate]
     three_q_ops = [ToffoliGate, FredkinGate]
@@ -86,10 +88,14 @@ def random_circuit(n_qubits, depth, max_operands=3, measure=False,
                 operation = rng.choice(two_q_ops)
             elif num_operands == 3:
                 operation = rng.choice(three_q_ops)
-            op_args = list(signature(operation).parameters.keys())
-            num_angles = len(op_args)
-            if 'label' in op_args:  # TODO: label is not part of gate params and must be removed
-                num_angles -= 1
+            if operation in one_param:
+                num_angles = 1
+            elif operation in two_param:
+                num_angles = 2
+            elif operation in three_param:
+                num_angles = 3
+            else:
+                num_angles = 0
             angles = [rng.uniform(0, 2*np.pi) for x in range(num_angles)]
             register_operands = [qr[i] for i in operands]
             op = operation(*angles)