Eigengate docs: move __init__ to class docs for better rendering (#5735)

Moving this up to the classdoc will provide for better rendering on quantumai.google.

Author: dstrain115

cirq-core/cirq/ops/eigen_gate.py

@@ -71,32 +71,33 @@ class EigenGate(raw_types.Gate):
     eigenvalue i and a part with eigenvalue -i, then EigenGate allows this
     functionality to be unambiguously specified via the _eigen_components
     method.
-    """
 
-    def __init__(
-        self, *, exponent: value.TParamVal = 1.0, global_shift: float = 0.0  # Forces keyword args.
-    ) -> None:
-        """Initializes the parameters used to compute the gate's matrix.
-
-        The eigenvalue of each eigenspace of a gate is computed by
+    The eigenvalue of each eigenspace of a gate is computed by:
 
-        1. Starting with an angle in half turns as returned by the gate's
+    1. Starting with an angle in half turns as returned by the gate's
         ``_eigen_components`` method:
 
                 θ
 
-        2. Shifting the angle by `global_shift`:
+    2. Shifting the angle by `global_shift`:
 
                 θ + s
 
-        3. Scaling the angle by `exponent`:
+    3. Scaling the angle by `exponent`:
 
                 (θ + s) * e
 
-        4. Converting from half turns to a complex number on the unit circle:
+    4. Converting from half turns to a complex number on the unit circle:
 
                 exp(i * pi * (θ + s) * e)
 
+    """
+
+    def __init__(
+        self, *, exponent: value.TParamVal = 1.0, global_shift: float = 0.0  # Forces keyword args.
+    ) -> None:
+        """Initializes the parameters used to compute the gate's matrix.
+
         Args:
             exponent: The t in gate**t. Determines how much the eigenvalues of
                 the gate are phased by. For example, eigenvectors phased by -1